1st off, that's very poor on the part of the seller to send a vehicle in that state - I would complain, at least to him/her if not Ebay.
2nd - Jetwash? Mmmhhh!!
With a new purchase you need to check every nut and bolt, so it's a good opportunity to strip it down.
YOU MUST REMOVE ALL ELECTRICAL ITEMS.
YOU MUST SEAL OFF THE ENGINE - there's the magneto, spark plug, etc.,
If the receiver, servo(s) are removed, Rx box, etc., you may even consider this.
Servos ARE NOT waterproof, particularly to Jetwashes. You can make them water resistant by various methods - see other threads on the subject.
If everything electrical is removed, engine included, then YES, GO FOR IT - FRESH START.
If not - DON'T EVEN CONSIDER IT!!
I'd certainly use a stiff brush if all is dry and carefully brush off where able, then use a DAMP CLOTH to wipe off the rest, then wipe dry/clean.
I think you get the general idea ... !!
Al.
