Hey, what do you guys suggest is the best technique to wash an 89' 929 engine and undercarriage? I need to know because I am planning on washing it because I have an oil leak and the engine and undercarriage are a mess so I want to wash it before I take it to the mechanic's shop to get fixed. Thanks guys, any tips would be helpful.

Well, I can offer what not to do, and that would be using a high-pressure coin operated type wash. Those will drive water into the electricals and give you no end of grief. You may end up stuck in the wash bay with a no-start condition too.
Best way is to wrap plastic around all visible electricals (distributor, alternator, starter, transmission connectors, sensors, etc.) and use a spray-can degreaser/cleaner first to loosen the gunk. Then hose off with a low pressure water source like a garden hose, carefully. You can detail as fussy as you want to be after that with more spray, small brushes, and rags.