Finn:
Try
some Marvel-Mystery oil. Its should be safer on the rubber
corner seals than carb cleaner.
Never
used it in a rotary but it did the trick for us when when had
sticky valves and ring in the Lycomings and Continentals.
The
secret ingredient is Wintergreen Oil (Methyl Salicylate)
that's both a solvent and a lubricant.
Additionally,
Valvoline Restore and Protect has worked well to free up
sticky oil wiper ring issues on late model Volvo engines that
have a known problem with overly tight oil ring groves.
"a
synthetic motor oil designed to actively clean engines,
remove up to 100% of deposits with continuous use, and
prevent future buildup"
Mike
in Maine