Having explored the forum I suspect I should have correctly posted in Muppet section.
JW no chainguard and it has lived in California, Connecticut, North London, Dublin and back to North London. It does pick up the usual okra hue in the winter. I will be giving the bike to my son-in-law, perhaps should invest in a new chain and send this one back to Shimano for analysis.
It is a bit of a cliche but mid 80's MTBs do seem to have been built tough - I have not lost a spoke, the wheels while not particularly high tech (36 spoke) are still original, as are the mechs. The tange frame has its share of scratches but still looks good and the scratches just have surface rust. There is no dishing which may help wheel strength. Only tyres, pedals, saddle and brake pads have been changed. So only disposables in 26 years - and it has gone off trail and down hill with its share of potholes at 40 mph.
I am looking forward to the RST as I expect a more refined, agile ride - and also expect it to be resilient. Only upgrade has been Deore brakes, and I will swap the Velo saddle for my San Marco Rolls.