sticky valve or

Old WW2 mechanic says he hears a sticky valve on my C-85 when I fire up for
first time in morning but can't describe the sound and says it lasts only as
long as a finger snap.

Wants me to add Marvel Mystery oil. I use Aeroshell 100 (50 weight) and
change it every 25 hours.

I can't detect any roughness upon initial start around 900-1000 rpm in front
of my hanger nor during the taxi a couple of minutes to a runup spot. On
throttling up to 1500 for the mag check, I notice a slight hesitation around
11-1200 rpm that goes away quickly and thought was just from the low speed
taxi.

Since I had to put a rental down about 7 years ago for a valve problem (per
the FBO), there is a little "pucker" factor regarding this conversation G.

Light Plane Maintenance book references "hand proping before first start of
day to find 'flat' cylinder". Not sure I can identify a rapid falloff in
turning resistance (books definition).

Concern doesn't seem to get to the point where the "cold cylinder" test is
applicable as doesn't last long (his finger snap).

Am I chasing nothing or what is a valid approach?

Thanks, Dick