Levinson 326S Volume Knob Loose

I just purchased a used 326S preamp and noticed that the knobs for input select and volume are loose and can be easily pulled off. It was cold when it was delivered so I thought when it warmed up it would be better which it did help a little bit, input select is now snug, but the volume knob is still pretty loose enough to slip on the main axle. I also noticed that the brass axle drum is shallower for the volume than for the input select, is this normal? 

Anyone else experience this?

agbrace OP: I know what you mean.  I like to fix things properly myself. Maybe the spring-loaded bearing is seized?  Lubricate? There is always epoxy (but permanent) or while plumber's tape.  Better option than electrical tape.

Personally, I would see if the entire pod is available and I would install a new one.  Can't be much more difficult than some patience, some screws, desoldering and soldering.

@ellajeanelle Thanks, the plumber's teflon tape was a great idea. A single strip around the brass drum allowed the knob to slide on smooth without too much force and holds it perfectly.