i have a 1991 350sd in very good condition,the bolt that holds the belt tensioner damper stripped out.is it safe to operate this vehicle with the damper disconnected and tied out of the way.thank you.

would not be as effective and would wear prematurely without the damper. There is a piece of hardware, maybe cakled a spider, that can be put in the stripped bolt hole so that you can tighten up the bolt.

my 1987 W124 230e. Was followed by awful, loud vibration of serpentine belt, belt tensioner shaking.

The cause was a nut and bolt that had come loose from where the hydraulic damper strut is attached to the belt tensioner. Removed shroud and fan, replaced nut and bolt, used Loctite, all good again. The thread wasn't stripped, thankfully.

I'd say try to reattach the strut. Your belt may be OK, but if the belt tensioner works loose it's moderately ugly. Mine was driveable (in limp home mode). Cheers.