Took out the output shafts to replace the bearings and, jeez, they had a super filthy layer of varnish on them. Very easily to clean up, but yeah, kind of gross. All were coated in sort of a black sludgy substance. I'm sure the rest of the inside of the TC looks like the output shafts did.

 

There are several options, the cheapest one by far would be to use diesel full in a parts washing tank of some sort, as long as there are no seals present you can clean metal parts this way. Some plastics do not like this so be careful if any are on or going to be at risk of exposure. The other option would be to use cans of non-chlorinated brake clean or crab cleaner, do not use chlorinated and never use any of these indoors if you value your health lol!

As far as cleaning inside the case that's harder since you would need to find a way to force the fluid to clean everything without risking seals, but this is nearly impossible without opening the case. Other than that you can attempt repeated fluid changes with a small (less than 20% total) amount of diesel added as a cleaner.