My K-series lasted 42,000 miles before I killed the big ends (I hadn’t done many track miles that day and forgot to check the oil ).
I bought it at 28kmiles, had a top end refresh done then (tappets and Exhaust valves). Only times I had to make use of the AA was when the alternator went, then when the clutch release bearing failed in France.
If looked after they will last pretty well.