Thanks all! I too have used Purple Power with mixed results. Also experienced the bad reaction with aluminum.
I don’t have a pressure washer, I’m always Leary of pressure washing stuff like this with the fear of getting water in it. But I know it’s a tried and true method.
I’ve also tried several foaming degreasers, gel degreasers, etc. I haven’t tried just a wash with Dawn, but I might give it a whirl.
I've hauled engines, transmissions & t-cases to the local car wash and pressure washed them there.
If they're real bad, I'll hit them with a couple cans of degreaser before heading to the car wash to loosen up the crud, then spray Simple Green after the pressure washer has cleaned most of it up. Simple Green is environmentally friendly, so it isn't bad to wash down the drain.... and it works great.
Far as pressure washing parts, just avoid any places that will let water by, seals, breathers, etc. I've had great luck cleaning up nasty drivetrain parts at the car wash.
Best thing I did was
build a heavy duty hitch carrier with tie down points. Makes it easier to load transmissions & t-cases and better access when spraying them off at the car wash.