Today I removed the variable capacitor, disassembled it, cleaned it (including ultrasonic cleaner with isopropyl alcohol to remove all the old flux etc) then reassembled with new grease and a tiny bit of deoxit on the sliding contacts.
Testing it out, it feels really smooth now :) BUT, my 100-250MHz range is still outputting 87.2-230MHz, it now stays leveled until 230MHz, but after that it unlevels every time (I can adjust LR40 to get me up to 233MHz maximum).
I just thought actually, I replaced some drifted carbon composite resistors around the place with metal film. Could they be having an effect if they are slightly inductive or capacitive?