Snowbum has a bit to say on this & also suggests consideration as to whether the tebnsioner & spockets are changed.
I changed the tensioner & smaller sprocket on my '78 R100RS.
I've a '91 R100GS. The cam chain was replaced not long before I bought it. I can hear it now & see the flicker in timing markls when I attempt to time it. I suspect that just the chain was replaced then, and other worn parts have contributed to its early demise.
My '91 R100GS thread is here
My Ride photos are here
It's just better when there's twins involved....