Could be wear in the pivot hole, and the pivot shaft, and probably the end stop on the mounting bracket. I had something similar on one and ended up drilling out and fitting a bush, and a blob of weld on the end stop.
RD 350 LC - 1982 - bounty like my bike in the 80's, finally got an original UK one. 31K/Aprilia RS hybrid - ex Yogi and Muttsnuts bike - my first hybrid Triumph Street Triple R (sorry!) ...and a box of bits I hope to be able to turn into a 1983 31K
Is it the whole stand that touches the exhaust? Or just the lug that the spring attaches to? I noticed a round dent in my LH pipe where the spring lug presses into it. But I have a suspicion that mine isn't a std stand, but 'borrowed' from another bike, as the bike sits way too far over on it and there is no retaining nut on the bolt (as per the parts manual), it just screws into a thread on the back of the stand.