I have a much-loved but rather ancient IBM-style Cherry mechanical keyboard which has suddenly developed some strange behaviour. Out of nowhere (i.e. no spills or anything), it seems to think that pressing *either* control key is also pressing a function key (usually F2 or F9) or even the Num Lock key. The fact that it's either of the CTRL keys suggests it's not just a case of cleaning (which I've tried anyway). Before I splash £130 on a replacement (because I really do love the keystroke feel for writing) can anyone suggest any remedial action or what might have happened?