Join Date: Aug 2015
Location: Pittsfield, NH, USA
It's a crapshoot how long they last. I'd probably leave them alone as long as none are broken (assuming you're not depending on it as your sole transportation to work, etc.). If/when a stud breaks, though, I'd suggest replacing them all as long as you're in there.
I bought an M900 new in 1993, and broke the first stud pretty much right away (horizontal cylinder, in 1995 at 19K miles). We didn't know yet this was a wider problem, so just replaced that one. Then a couple months later another one broke (also horizontal cylinder, at 22K), so we replaced them all (I thought). Due to a miscommunication, I thought that we had done all 8 studs then, but he just did them all on that cylinder. 16 years later (in 2011 at 196K miles), I got a base gasket leak in the vertical cylinder, and in repairing that, found that that cylinder still had the original studs, so replaced those then.
1993 Ducati Monster M900, bought new, 265K miles, killed by minivan 30Oct17. 1995 M900, was ex-wife's bike, now mine again.