So just reply to them with your subsequent questions. They'll be able to tell you if the out of warranty repair includes the cost of the part you need replaced.
Alternatively I suppose there might be a small chance you could find someone selling a very old and used or even broken HD650, for cheap, that you could get the part you need off of.
thanks dude i'll e-mail them again. i have been watching eBay for spares / repairs but none ever turn up, not surprised as after hearing them you wan't to take care of them. Their was a broken HD 600 but that was going for £40 or so, not much more for a potential overhaul from senn.