Hey notasnob (yeah, right ;D)
I think you may be right re the control knob as while ours never played up completely it did seem to go a bit haywire once in the same way then corrected itself. Worth having a lash at anyway - cant sell it like it is huh?
With the drip tray leaking, had exactly the same issue with ours. Stuff just doesnt collect properly. Most annoying and doubt you will get around that one.