Head stock bearings wear at around 40,000 miles, replace with taper roller kit. Old bearing shells tap out quite easily with a mallet and soft metal drift unless they are already taper roller type. If so run a bead of weld to the old shell to allow you something to tap against.
Swinging arm bushes wear at up to 40,000 miles. If any play is felt at the rear wheel - replace. These composite bushes are easily removed with a metal drift and hammer. Knocking in the replacements with a soft headed mallet may cause the composite material to crack, better to use a length of studding and some large washers to just wind them in, turning the nut gradually with a spanner till seated. See also:- pattern parts
Wheel bearings, the retainers need special tools and therefore may need replacing at around 40,000 miles due to lack of lubrication. My bearing retainers were removed resulting in stripped threads. The two aluminium components welded together over years of neglect. These are not left-hand thread as someone told me at the time, so if they won't move consider spark erosion or replacement hubs if they are available.
Rear chain life depends on use/lubrication/cleaning routine etc. Around 6,000 miles is normal. I'm using RK heavy duty type, excellent with little adjustment needed. O-ring replacement would require much less attention/cleaning/adjustment - however the pin length on most o-ring chains does not allow sufficient clearance to the engine crankcase, take care, I understand Reynolds may have a suitable type?
Steering lock is often damaged from attempted theft. File the head off the retaining rivet, then use the key to remove old lock. In the event of the lock being snapped off in the locked position and no key available, carefully drill out the old lock. The new lock is held in place by a one way rivet and suitably sized washer.
Powder coating in gloss black provides the best finish I know of after first shot blasting & inspecting the frame assembly.
Fuel tank often corrodes at its base near the welded bottom where water can collect. Use petseal or replace as necessary.
Stainless steel machined footrest/engine hanger as well as many other "machine specific" fixings are available from Inox Fasteners. Their website has a wonderful technical section on stainless steel, worth a visit.
Exhaust system is short lived, around 20,000 miles is normal. Make sure the drain hole near the collector box remains open. Some owners drill another drain hole at the lowest point of the collector (near pipe 1) to help with drainage.