On a 1983 500SL

My car has a distributor with advance only, no retard. Specs are for 16 degrees BTDC at idle, 25 degrees at 3000 rpm. While idle is fine, I'm seeing 35-40 degrees even BEFORE 3000 rpm!

I disconnected vacuum advance from my distributor to check a vacuum problem I'm having at higher RPM's. At idle, the timing gun shows TDC, but as I apply more revs, the timing mark MOVES as well, towards more degrees BTDC, about 10-15 degrees. So this is why at rpms the advance is way too far off, something is compounding on top of the advance curve.

Looks like something is advancing the timing EVEN with advance totally disconnected. What could be doing this? Is this normal? I would have throught it would STAY at TDC throughout rpms when vacuum was disconnected.

What could be causing this??