One of the main slider pots on my 244 stopped working a few years back - no crackles or warning, just no effect and no sound on remix or recording. The same has happened to another one - so only 2 of them work. Any ideas how to fix this? I've tried cleaning them and no effect. I'm not used to pots suddenly failing! There is a signal going to them but no output from them. It seems a bit of a job to replace them.