Morris Minor Owners Club

Hi folks,
The dizzy in my car is a Lucas 25d.
The vacuum advance unit has been replaced at some point.
A suck on the pipe holds vacuum, but it does release slowly. Is there anything to do on this? Historically i have always found them to return with a little *thud* when you release/stop sucking), so wondered if this was anything to look at from experience?
Thanks in advance!

Screw holding the capacitor too long and snagging on the baseplate? Can happen if the washer is missing.

A good suggestion, but no, it does this with ignition kit fitted and removed.
Any other suggestions?

Give the internals a good spray with WD40 or similar.
It may just be the turning plate sticky on the fixed plate.
Worth a try at least.