I wish my M103 had a steel spring tensioning element rather than the hokey rubber bushing. It would save M103 owners a lot of grief.

If item 17 is a "pivot" rather than a lock bolt as in the case of M103, and the tensioner is free to rotate about this pivot when torqued to spec, then a good lubricant would be graphite, which is an excellent lubricant for high load low velocity sliding surfaces.

A convenient form is Lock-Eze, which is an emulsion of spherical graphite in the petroleum distillate carrier that evaporates. It's available at most hardware stores.

If the belt vibrates you might also try replacing the spring in addition to the damper.

Duke