When I put a spare motor in my 924S, the motor had been sitting for 5+ years. There where a couple of lifters clack badly. I mean LOUD. My 944 ticks loudly when it sits in the off season, but nothing like this. I tried an oil change to thinner 5w-30. No difference. Letting it get up to temp and driving it didn't fix it either. I thought I'd try some Marvel Mystery Oil before pulling the cam tower. I added it and 30 seconds later, the noise went away. I ran the motor for 15 more minutes, drained the oil, and filled with fresh oil and a filter. Ticking never came back!
Additives can work, but don't use them and leave them in the oil--a oil change is a must.
-bj
