Suggestions how to repair these

I have a pair of JPW Powered Monitors (1995), Made in UK, perhaps in one of the last production batches before the company was acquired and moved production in the Far East. Bought brand new for a PC-based audio back then but used it intermittently for couple of years only and stored them for several years in its box. Took them out recently and I'm still amazed at their soundstaging and imaging particularly if mated with a sub. I really like them a lot. However, a couple of things need to be fixed.

1) The volume pots are stuck at 9 and 10 o'clock positions and don't move at all. For now, however, I'm using the source's volume control but eventually I'd like the source at full volume and adjust the speaker's volume controls. What caused it to get stuck? Is this a common occurence when left unused for long periods? Is this something I can repair myself or should I just bring them to a qualified technician? What needs to be replaced here (or cleaned)?

2) White spots/residue (not dust) have developed around the baffle and cone areas. There's no effect whatsoever on the sound but I'd like to remove and clean them. Can you suggest the best and safest way to do this? Any specific cleanning material?

For visual reference, please take a look.

Everything else are perfect - cabinet, grills, etc. are spotless and clean like new. Sound quality, as mentioned, is spectacular. But these two things bother me and would like them fixed. Any helpful suggestion or recommendation would be greatly appreciated. Thanks.