I have both a 4 (with the original circuit board and no battery drain issues) and a 4ti. They're interchangeable as far as I am concerned - I seldom use flash and don't have an F280 anyway. The weight difference is negligible. I'd stick with your 4 and get it CLA'd.
2 black om4t's bodies went for $180 last night. I fell asleep and missed it.
Well, I'm pretty sure I've seen those same two bodies sold about a month ago (I recall one was damaged exactly the same way). They showed up for sale once again - not a good sign. Something tells me they may not be repairable.