Warm engine up, allow exhaust to cool.
Spray with Jizer (or whatever)
But avoid spraying alternators or starter motors directly.
Any really bad areas, work in with a brush.
Allow to soak in, then jetwash. (Use the "Fan" spray rather than the fine HP jet) Again, only lightly spray Alternators and Starter motors (You do not want to wash out any internal oil/grease)
Avoid directly spraying any electrical connectors (Ordinary wiring is basically OK, but avoid directly spraying large bundles where water might get in and take a long time to get out again)
Leave to dry from engines heat with bonnet open. (If you have recessed areas like the spark plug access remove plug leads and check that no water has got inside, If it has, do whatever is appropriate to remove it and leave the leads out until engine heat had dried everything out)
Put any disconnected leads back and Start engine and check that everything is OK.
Over the next week or so check engine bay to see where the oil was coming from so that you can work out what needs to be done to fix the leaks.
I have done it this way for decades, never had a problem.