Really cannot answer that question. All depends on maintainence and how it was rode. There are lots of factors in here....
I had a 1984 FXRT and it had approx. 89,000 miles on it. The only thing it needed was cylinder base gaskets though. The bore, heads, and top end were in great shape. I put it all back together and rode another 20,000 miles and then sold it.
My 93 was rebuilt (top end) at 50 k. Today, at 76k it runs fine, but does burn about a quart per 1500 miles or so. Depends on how hard I twist the throttle.
Ran 76,000 miles on my 99 EVO before I sold it.Installed an oil cooler and ranM-onesynthetic changed every 2500 miles or under. Basically, I never let the oil get dirty which is the 1st commandment of owning British bikes for several years.No mechanical issues with the engine whatsoever.I'd swear the bike ran just as goodas the day I bought it.