I brought my 2007 328Xi to the dealer, they cleaned my engine for $50. It is beautiful in there now and it was disgusting.
Edit: where I was going with this, I assume they know what can be sprayed with degreaser and water. For peace of mind, I'll spend the $50
I had an oil leak coming from the eccentric shaft sensor. I guess it's pretty common, search for where it is, idk myself honestly, but it would be something to check.