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Replacement pots "can" be found from some suppliers. Original potentiometers use a thin and somewhat flimsy shaft size. They used to be available in plastic or metal (better choice) but are pretty hard to come buy nowadays as are the matching knobs. There are plenty of "parts brokers" out in the world who seem to do a good job hunting down many old components. Do a search on the net and send out a few emails, you never know your luck.
I agree with Jesper on the battery replacement, if possible go for a replaceable lithium arrangement BUT YOU MUST modify the original circuit to remove the charging capability or you will blow the lithium battery up!! The mod is simple and requires you put a "blocking" diode in series with the battery positive. This will allow power from the battery to feed the SRAM but will block voltage from being applied to the battery.
As to capacitor replacement, yes a contentious issue. Certainly I always replace any caps relating to the PSU side of things. These cop the greatest hammering and depending on the quality, will no longer be within original specs. As to the rest of the circuitry, everyone seems to have there own views ( a bit like climate change..lol). It is true to say it is pretty pointless to simply replace ALL capacitors just because they are old. It is akin to putting a new engine in an old car when really a simple tuneup would suffice.
You need to replace those that are affecting the performance of the device. IF you get to a point where that may be 60 to 70% of the originals caps, then sure it wont hurt to go all the way, but don't do it simply because you can.
Simmons schematics, the old chestnut. The originals floating about are generally poor. They tend to be "cobbled" together, old early revisions, missing bits, user modified, manual merchant stamped and simply incorrect documents of garbage (well that's my view anyway) There are some good copies around but you will need to go to the source of those to get them. Some group members have gone to the time and effort to manually trace and redraw schematics of some simmons gear and these docs are good. If you are looking for good SDS7 service info, next time you go to the crapper, don't flush the paper, use that to do your fault analysis. What you will see on the crap paper is far better than what you will see reading the available SDS7 service manual.