Chasing a potentially bunk Youtube video I tried out ATP AT-205 on some hard rubber parts a few days ago. Parts were the bushings between the tank and frame, one seat rubber, one engine fin rubber, and the speedometer bushings. I initially poured the AT-250 into a plastic container, and then realized I'd made a terrible mistake as the AT-205 began to take apart the container, fogging the plastic and actually causing cracks. Into a glass jar it went. 

After about 24 hours the rubber was actually rather supple and pliant again. I'm impressed. The AT-250 is a darker colour now. I feel like it might have lost a bit of it's magic eating the plastic container, but the rubber parts are still way better than they were before I put them in. No swelling, just more... rubbery. 

Remains to be seen if they just harden up again but The Internet (unreliable at best) reports that since it's mainly a plasticiser most reports are that the rubber stays in good shape afterwards.

Is it AT-250, or AT-205? 

I've used the ATP AT-205 in engines and transmissions of old cars with leaky seals and it's pretty amazing stuff.

Sorry yes, it's AT-205. I've chucked the hard front tank bushings in the jar as well as the turn signal flasher holder. It's looking brown and ugly in there and I still think the plastic did something to weaken the mixture. Might have to get another bottle for science.

Interestingly, I don't think it did much for the engine fin rubber damper I tried out. It's maybe... 20% softer than before after 24 hours. Either the mixture is weaker or that rubber is just too far gone from heat and vibration.

Thanks for confirming. 

It did wonders to the turn signal flasher holder but barely anything to the tank rubbers. Seems like either the magic juice isn't as magic as before, or there's a rough correlation to how abused the rubber is (like the engine fin rubber) and how well it takes to the AT-205. Granted, nothing has sat in the jar longer than 24 hours because I'm impatient, so maybe it does better on harder rubber with time.

Also fair warning, this stuff eats paint. Make really sure your rubber is completely clean before reinstalling.

I had some old rubber tyres from a Meccano/Erector set that were pretty hard and brittle with cracks in them. I soaked them for a few days in brake fluid. They all came good, except for a couple that were too far gone. I also read that putting them in the dishwasher works too. So I threw them in there afterwards to clean up the brake fluid residue. Came out fine.

Diethylene glycol monoethyl ether