Robert W. Roe:

As far as the cleanliness of transmission internals go, transmission fluid is an exceptionally good cleaning agent (next time your hands are thoroughly black with greasy crud, try rubbing some transmission fluid on your hands, then wipe them off with a rag -- you'll be amazed).

That being said, there is some accumulation of varnish in certain areas such as the friction materials in bands & clutch packs. This is actually the reason why I used a very brief dosing/exposure of "super sealer/rebuild in a can" in the example I gave in my prior posting in this thread. It wasn't really so much to soften the seals (which in that case was actually a little bonus) -- it was primarily meant to help clean off the varnish accumulation. Those transmission snake oil treatments have some solvents in them, which helps to put any crud into suspension so the filter can take it out. It works as a good "pretreatment" if your transmission is in marginal condition to begin with.

Synthetics in general are EXCEPTIONAL products. I can give you an example: back in the early '80s I was running some showroom stock VW Rabbits & GT 3 Sciroccos in SCCA racing. The front wheel bearings took a tremendous amount of abuse & needed to be replaced fairly often. These bearings are large sealed roller bearings. I disassembled two sets of bearings, cleaned out the stock grease & repacked them with Amsoil synthetic grease. Results: those two cars went for almost an entire season without the need to replace the bearings. Truly amazing if you ask me. Mobile One is phenomenal stuff as well -- if you've ever opened up a high mileage engine that has used it religiously, you'd think that you're working on a brand-new engine! ..Nuff said…

RTH