2003 Volvo Penta D2-55 Saildrive symptoms

[Boaterbob]

Boat is 2004 Bavaria 41. I am new owner Spring 2016. Ran flawlessly for 2 week Summer cruise.

New observation yesterday when running engine at dock: apparent slippage (lack of power delivery to prop inferred by prop wash not increasing with RPM) of sail drive clutch. Very cold day with ice around boat, water temp probably 35-40F. Previous power applications at dock have shown huge prop wash at 2000 RPM with no sign of "slippage".

Today I try it again and cannot see a problem. No sign of "slippage" at 2000 RPM!
So is this a "symptom" of a developing problem?? The sail drive was allegedly "serviced" Fall 2015 with new rubber seal. Not sure what else. Only 500 total hours. Oil looks good in sail drive but I will replace it anyway.

Could this be due to me sailing in neutral, not reverse (which seats the conical clutch I read)?? Could it be temperature related (surface ice half inch thick).

I am inclined to change the gear oil and observe. Any insights from experienced Volvo sail drive owners?

Bob
Olympia, WA