126 - Sticking lock knob

[S-Class Guru]

The passenger side lock knob on my '91 300SE is hard to pull upward. It pushes down just fine, and the key works fine in both directions. And the vacuum supply seems good; it just can't overcome the resistance when trying to move the knob upward.
As a result, the vacuum actuator has a hard time getting it all the way up, and the alarm sometimes goes off.
You can watch the knob when you hit the remote; it comes up an inch or so, then pauses, then pops another 1/8 inch. All the other locks work fine.

Is this probably the lock mechanism (big bucks!!!!)? Or could it be the vacuum mechanism dragging in the "unlock" direction?

Anyone have this happen; got an easy solution?
I tried spraying lube in the keyhole, and even down the lock knob shaft - silly me, I know I'm gonna have to take the panel off

Tks,
DG