Water leak diagnosis....

I posted previously my dilemna with water accumulating in the lowest part of the cabin of my 90 500 SL, under and behind the passenger seat. The result was terminal damage to the power seat controller for the passenger side [clever engineering placement of this sensitive component, eh?]. This water problem was encountered ONLY after removal of the hard-top and use of the softop during a two hour drive in a rainstorm........so the suspicion has to do with the softop. Problem is......my mechanic suspects the leak to be a small (1/4-1/2 inch) break in the rear window plexiglas window. I am unconvinced that enough water could flow through that small break to have created the "flood". Additionally, once I absorbed 6-8 bath towels worth of water from the carpet the initial time, I had a re-flood on subsequent days, even though there was no additional rain to which the car was exposed. So, I suspect that water accumulated and being reserved/stored somewhere else, then flowing into the area again. This happened twice in three or four consecutive days.........Any ideas, either about the probability of a small tear in the window being sufficient entry point for such a significant accumulation, or about other possible entry points? I know I've asked before, but I'm almost ready to trade the car, imagining that I have an unsolveable problem........replacement of the power seat controller was over two hundred dollars just for the part, and I'm not willing to risk destroying another unit. My shop is suggesting either a total top replacement or just a rear window replacement, either of which is an expense without guarantee that it will solve the water problem.......I'm frustrated to say the least.....any help will be appreciated....