My DT400 has developed an Oil Leak from the red circled area in this picture.  I can't find what this is.  Is it a Shaft Plug or something?  Most of all; How do I go about fixing this?  It is just under the Drive Sprocket. Thanks.  

 

I'd think it'd be a bung on the end of one selector shaft. be unusual to leak.

My 250 did the same thing

cliff

See #19 in this diagram.  www.partzilla.com/catalog/yamaha/motorcy...fter-1-250b-c-400b-c

The strange part is that looks like it might be the end of the shift shaft?  If so, there is no room for the plug.  It also looks like someone has been tapping on the end of the shaft?  That seems like it would require #16 to be missing and that the sector gear 20 couldn't be on the shaft all the way?  Maybe someone used a different plug than original which if I remember correctly was coated in black rubber like the ones at this ebay link: 90338-10063 plug ebay

Great info there thanks MarkT.

Thanks for the information guys........very helpful. I was curious about those "tap marks" also, but was not going to worry about them unless someone else brought them up.

This is strange to me.

What I would do is move the shift up and down while watching that spot...  or maybe put your thumb over it...  look and feel for movement while moving shifter in and out and shifting in and out of a few different gears...  probably have to roll the bike a little to get it to shift up into higher gears with engine off. 

If the silver thing in the center moves while shifting, it probably is the end of the shaft (even though that seems unlikely) and further investigation might be needed.  If not, clean it up good and apply a coat of RTV silicone sealer over the area and see if that fixes it?

Thanks for the help and advice. I thought about trying the RTV ....... and even "JB WELD" crossed my mind for a moment. But looking closer at it and comparing pictures on ebay of Crank Cases, it looks to me like that small portion of the casting that holds the plug you mentioned broke off somehow.

Unless there is a fix for that, I'll probably have to live with the leak or replace the left side case, which I have no experience with.

I'm still looking for options; and open for suggestions and ideas. Thanks.

Ahhh...  that makes sense.  If piece of case is missing then a good sealer or epoxy would be worth a try. 

Thanks for your help clearing things up on this. I now have a direction to take on stopping this leak.