While looking for the source of metal pieces in the transmission oil I stated inspecting the gears. From a foot and a half away they look great.  Looking closer they look a little beat up. 

Are these too worn?

link to google photos album

They look a little dirty but I wouldn't be very concerned about the horizontal grooving on the faces of the gear teeth. The process of manufacturing often leaves markings like this. What would be cause for concern are areas of deep wear, which will show up as pitting. Damage such as chipping may be evident as well but this is unlikely. One good way to determine what is wear and what is left over from machine work is by comparing both sides of the teeth on each gear. If the loaded side of the tooth that is transferring power looks the same as the back side of the tooth, negligible wear has occurred.

The shift dogs are the most common place for wear and damage in a two stroke gear box. Looks for rounded off edges on the dogs and the gears they engage. The gear seats on each shaft are constantly meshing but the dogs move in and out of position to change gears, during which time there is a significant difference in the rotational speed until the gear fully engages.

Generally, if the bearings are good and the box has never been run dry it's not likely you'll find anything wrong.

I expanded the pic up big--bad idea lol.
There's is 'some' wear taking place where the teeth roll over each other & can see a pit hole in one at top right in pic possibly breaking through the hardening or something got trapped there.
Visible dogs look ok but as said they get round edged when worn on the two parts.
Done a lot of rotation in 50 years but i think it'll do a few more so don't worry yet.
In my opinion that is--me who hates spending money!!.

Here's an extreme case of what is possibly starting on some of your teeth.
Just a random google pic i found to illustrate breaking through the hardening.
photos.app.goo.gl/vubt8s74HwZW5mWR6

I see the same thing, but if it's what I think it is it should wipe right off.

Check bearing cages and little needle bearings carefully and make sure snap rings/shims between the gears are all there... looks to me more like some debris ran itself through the gears?

As with everything, it depends.  It depends on what caused the pitting.  FOD and corrosion pitting as long as it is not serious, would not concern me.  My 175 has light corrosion pitting on some gears.

Without doubt, those gears have seen some serious action but the pics are not clear enough to assess the cause. 
The biggest concern is the sliding gear, from what I see it is starting to spall in a few places, but as said, what I see in the pics and what I would see if the gear was in my hand could be two different things.  I would be concerned though. 
From what I can see, 90% of the damage is FOD. It is too random to be surface fatigue.

It also depends on availability and cost of replacement parts.  If a used complete cluster is available in good condition and for not a lot of money, I would change if for peace of mind.  Daft not to when the engine is apart.

Bear in mind, if you change a gear pinion, you also have to change the corresponding gear wheel.

It also depends on usage.  At work, I would assess some of the gears to be "on the way out" and discard them.  I would give them a useful life of less than six months before failure.  Your transmission however is not being used in a 100 tonne dump truck running a 24 hour operation.  Again, this is only what I can see from the pic.  

A lot of things to consider.  If I were to highlight any points in this post, I would pay particular attention to paras two and three.

To cut to the chase without beating around the bush and humming and hawing: 

Are those gears worn and damaged?  Yes.

Would the manual say replace any worn or damaged gears?  Yes.

If lightly used for short rides every other sunday, how long would those gears last?  Probably many years, but they will only get worse.

Would I change them?  We go back to para three.  I would give it a little time to source a used complete transmission, rather than immediately put the old one back together.  But that is just me. 
I build for future generations, not the present.  I build them with an eye on the next guy doing the next resto on the bike in fifty years time when parts are impossible to find.  Change a slightly worn part now and it will still be good for the next guy and one less headache.  
Used lightly, your gears have probably years of trouble free life left.  It really is down to you.  

 

Thanks everyone for the information. I think I can pick up separate new-old-stock parts on ebay on the cheap. I intend on keeping this bike forever so I will do what it takes for it to last forever.

I cleaned the axle and gears and added some more photos to the google album, If anyone was curious.

p.s. I had to look up "shift dogs" and "FOD" (foreign object damage). I've been at this for three years and I still have a lot to learn. Everyone's input is very appreciated.

Be aware that if ya replacing gears on 'that' shaft then the small end gear is press fit.
Not sure if it'll go back on as tight as it came off.
Be interesting to know if a new pressed gear measures a gnats whisker tighter.
If it lets go you'll have no second gear. that's all.
Had that happen to a Yamy V90 scooter in the early "70's which was just bad factory tolerances on an 'as new' 'almost new' scooter.

I found a nos main axle, so I won't have to worry about a loose fit. It came with three of the four gears required.

I've been slowly receiving nos gears and some have arrived with surface rust, which made me wonder if the original gears have a coating on them to inhibit rust and if I sand off the rust will the untreated sections be more vulnerable to corrosion.

I sent the crank to be checked out. They, (Crankworks), recommended a new connecting rod and offered a "Vintco" package. Are there any reasons to not want a Vintco rod?