If you look after your Shergold, it will see you right for a long, long time.
My main Shergold, a 1976 Modulator which I bought second hand in 1993, has had many hours of playing in its life with many dips and flats in the frets, and large chips and cracks in the body finish, but is still the most enjoyable and best sounding guitar I have.
I end up using it 9 times out of 10 for general playing in preference to my PRS Classic, the only exceptions being where I need the high gain pickups and trem.

These guitars need very little maintenance.
The fingerboards on almost every production model are sealed, so there is no need to use oil on the finger board. Unlike F*nders of similar age and usage, I have yet to see a Shergold that has had the sealant worn off the fingerboard.
Necks are made from high quality, hard maple using a seperate maple fingerboard to cap the truss rod trench in the neck. Some guitars were made with rosewood fingerboards, but these are custom built examples only, or late (and limited) production runs (eg Activator and Nu Meteor).
The bodies are made from Obeche (sometimes called wawa) though some later examples are swamp ash or use a maple and mahogany laminated centre section, almost all are finished with a poly coat finish over the whole surface. So no exotic care is needed there, but they do suffer a lot from finish cracks.
From experience, I have found that ordinary spray-on furniture polish, applied with a household duster, is by far the best way to clean these surfaces. This will usually shift dirt build ups around the frets as well.

One problem I have had with nearly all my Shergolds, is with the output jack socket. I have had to replace these on most of them, but I suppose that is quite reasonable considering how long they have been around!
Important Note on Jack Sockets: If you need to replace the socket and you are not very adept with a soldering iron, or don't fully understand the pickup switching circuitry, do not attempt to rewire a stereo output on a Shergold. Stereo output sockets are fitted to all Modulators and one of the two sockets on Custom Doubles.
Go see your local guitar shop repair man and let him do it. At least if he gets it wrong you can bitch at him about it! I have seen many home-grown attempts at rewiring the stereo jack and they are almost invariably wrong! Hopefully, the work I've done on documenting the circuits for the Modulator Modules will make bad refits less common.

The truss rod on all Shergolds is a "double acting" design - this means that the neck is manufactured to be flat when no tension is on it (in contrast to most other guitar necks that are made with a slight backwards bow). So once it is strung the neck will tend to bow forward - this is then corrected with the truss rod. The benefit of this design is that the truss rod is pulling the neck back, rather than the neck trying to pull the truss rod forward as is the case with normal necks. As side benefits, it is much easier to manufacture a dead-flat neck than a slightly bowed one, and the truss rod can be used to correct distortions in either direction - something that is pretty much impossible with a standard rod.
Note that as a result of this design the Shergold truss rods are much more responsive than other makes - use smaller and more cautious adjustments than on a normal neck.
On early Shergold necks there is no obvious adjuster for the truss rod - later models have a headstock end truss rod cover that makes adjustment a simple tweak with the approriate hexagonal key (5/32" - a slack 4mm key might do the job, but the correct imperial size is the best fit). On older necks (typically pre-1978) the truss rod adjustment is at the body end of the neck, and can be accessed by removing the serial number plate at the heel of the neck. A slim bar (a small size sturdy screw driver or long handled hexagonal key work well) can then be inserted into the holes drilled into the adjuster barrel at the bottom of the access slot, and the rod tweaked gently by turning the nut using the tool as a lever.

A common error that many guitar shops and less experienced owners make is damaging the bridge piece adjusters on later model Shergolds. The heavy bridge used on Modulators and Cavaliers is easy to adjust with the Philips head bolts at the back of the bridge moving the bridge pieces backwards and forwards.
The (nearly complete) gallery of Shergold bridges shows the different types commonly fited.
The more modern bridges are made of a single piece of sheet metal with the ball ends passed through holes in the folded section at the back of the bridge. The bridge pieces are small grooved "barrels" with a bolt running into them from the front fold of the bridge.
The correct way to adjust these is not obvious. Most people, including otherwise good guitar shop repairers, try to adjust the bolts from the front. However, the bolt heads are tilted down towards the body, and are obscured by the bridge pickup mounting. The usual result from these attempts is stripped-out heads on the bolts, and gouges in the plastic pickup mount.
The correct way to adjust these bridge pieces is from the back, that is from the side of the bridge where the strings are anchored, using a 0.050" (1.27mm) hexagonal key inserted into the hole in the back of the bridge piece, into the hexagonal socket cast into the tip of the adjuster bolt.
Some earlier examples don't have these hexagonal key sockets - the best way to adjust these is to slacken the string off and turn the barrel while holding the screw static.