I'm trying to remove 40 years build-up of oil & dirt from a kombi transmission. This stuff laughs at high pressure hot water & just clogs my wire brushes & flap wheels. I'm having a bit of success using a hot air gun & scraping but it's very slow. What's next- an LPG torch & burn it off??

Yes, That's also been my experience. Lot's of Kero, and plenty of elbo grease. I also find a good blunt knife or paint scraper does a good job without scratching. Once most of the gunk is off, it's then a wire brush or scouring pad ( the stainless steel kitchen type).
Andy.

Theres is NO easy way to clean off VW gearbox gunk.

just plan to be there with a blunt knife, scraper, screw driver wire brush and ELBOW grease for afew hours.

preferable somewhere in the shade. I usually do mine in the afternoon down the side of the house... when the sun has gone over... nice n shady

I suppose our 2 litre box wasn't 40 years of gunk, but I found a really easy way to clean it.
I got the wife to do it!
She wanted to help a couple of years ago, and so I said 'this is your mission should you choose to accept it'
She did.
Thanks Fleur

Peter

i used a screwdriver and a paint scraper thing... and i used newspaper, still got a couple of crap black marks on garage floor tho