I recently picked up a Marshall 4001 Studio 15, built in 85 and original except for the tubes. It has some damage to the knob and some were loose. Also, the volume pot is intermittent. I pulled the knobs off and was able to spread the gap in the shaft's enough to get the knobs back on snugly. However, the volume pot is still intermittent and cuts out until I jiggle it to where it will work. One other is a little scratchy, but after working the other a bit they seem to be fine. I pulled the chassis and it looks like the pots are attached to the PCB. They are also gold in color and appear to be Marshall branded. So, is it possible for me to obtain replacements and install? Are there other options, like spraying the pots with some kind of cleaner and if so, how is this done? Second issue is with the speaker. It's in good shape, almost looks new, but the dust cover in the center of the speaker has come lose and was laying in the cabinet. The amp is really dusty and dirty and appears to have set for several years. Does it hurt not having it on? And if I can just re-glue it what type of glue should I use. I'm not crazy about the Vintage 30 speaker, but these are becoming collectible amps and to keep it original I'd like to get this speaker at least to where I can install if needed. BTW, any recommendations for a good sounding speaker for this amp. Something that would take the top end and add some nice (not flabby) bass? Thanks so much.