It does NOT sound like anything is wrong with the preamp's circuit -- so, no serious issue.
More like a contact problem with the volume pot. Contact cleaner spray would be useful -- but you'd have to apply it on the inside of the pot, on the contact surfaces, with the amp switched off, of course. Then turn the volume up & down a few times to clean of the contact surfaces.
Changing a volume pot is not an expensive undertaking -- if it comes to that (you'll have to use the same value replacement pot, of course). It might even improve the sound if you opt for a quality pot!
More like a contact problem with the volume pot. Contact cleaner spray would be useful -- but you'd have to apply it on the inside of the pot, on the contact surfaces, with the amp switched off, of course. Then turn the volume up & down a few times to clean of the contact surfaces.
Changing a volume pot is not an expensive undertaking -- if it comes to that (you'll have to use the same value replacement pot, of course). It might even improve the sound if you opt for a quality pot!