SME 312S issue

Have a vintage SME 312S arm mounted on a Technics SP10 MKII sitting in a Porter Plinth with a Kiseki Purple Heart cartridge and I and all others that listen to it hear mistracking at times in the final third of most standard LPs. Since it is happening on just about every record I do not believe that this is solely inner groove distortion. The most common theory(since the arm and cartridge was set up by one expert and then adjusted by another) is that upon close inspection, the bottom of the arm tube may be brushing against the top of the arm lift. The lift has been adjusted so that it can go no lower and I can find no information that seems to show that the arm can be adjusted independently of the lift(they seem to share the same platform). When a light is placed behind the platform and shone toward a viewer the gap seems smaller when the cart is down on a stationary record near the end than compared to the gap visible when the cart is down near the beginning. ASSUMING that this problem is being caused by this rubbing, I ask if anyone has had a similar experience, can tell me why the gap may be smaller toward the end of the record(manufacturer or installer error?),and what possible solutions(short of taking an exacto knife to the rubber pad on top of the lift or grinding a bit more of the curved area at the bottom of the arm away) might be possible. Have a friend with a near identical set up that was here listening today that will look at his gap tonight and report back. Have also sent an email to SME. Many thanks, LS