I had a 1982 R100RT, full-fairing touring model that was stone reliable during the 10 years and 30,000 miles that I had it. I sold it to a friend who still rides it and last I saw it was approaching 80,000 miles. It only stranded me once, when it was new, after rivets improperly installed in the clutch plate during manufacturing pulled out. I crashed it once and rebuilt it as an R100CS, sportier with only a headlight fairing.

You must check and adjust valve lash at regular intervals. This is very easy to accomplish with feeler gauges and hand tools. A properly-adjusted valve train on an 'airhead' makes a finely-tuned clicking sound. The valve train, particularly the exhaust valves, becomes 'tighter' as it wears, and if it sounds quiet it is too tight, possibly due to a lack of maintenance. If the exhaust valve becomes too tight you can 'burn' a valve. I had no such trouble in 30,000 miles. If a valve or seat does go bad, removing the head is easy since it is conveniently right out there in the open. A bit of machine shop work to replace the valve seats, and back on they go. They can be R&R using hand tools and a good torque wrench...

Carburetors sometimes need to be 'synchronized' (not often, though) so that left/right manifold vacuum is equal at idle and light throttle. This is relatively easy with a set of damped vacuum gauges. I did it a few times by comparing left/right readings using one gauge, but I don't recommend this method...

BMW recommends replacing brake fluid annually, which is simple DIY stuff.

Oil and filter changes are very DIY. The RT and RS models use a cleverly hinged filter so that it can be inserted and removed without removing the fairing!

Air filter change is also DIY, just pop a few spring clips, remove the old, insert the new.

My personal style preferences are the sporty "RS" model that has a very effective fairing with a short windshield, or the "S" or "CS" with the headlight fairing. The "RT" touring model with full fairing and tall windshield was not quite tall enough for me, but then I sit taller than average.