Re:compression, seems all gauges are off, even snapon Most techs agree that what's important is that the cylinders are within 10% of each other. The surging could be the micro filters in the carbs. Many seizures and or partial seizures are caused by plugged or partially plugged micro filters. You can also eliminate a faultering pet cock by running the line to the carb straight from the fuel pickup, (the diaphragm in the petcock becomes mushy and unfortunately is non replaceable). If your intermittent problem disappears that saves you removing and cleaning the carbs. Gray fuel lines definitely will eventually become a point of concern. If you can remove the inline at the carb, and you see green mush, than probably that is also in the micro filters and narrow carb orifices. Re: colour and type of oil. In our race ski (800 cc LTD at 7600 rpm, we used the cheapest synthetic oil that wasn't clear. We have been using Shell Nautilus for years, and the blue colour makes it easier for us to see leaks. The OME is a fortune and BRP doesn't make its own oil.i Sometimes, Walmart sells tc w3 synthetic for sleds in giant 5 litre containers for $40 ish. I'm always having a peek at their oil shelves during off season for bargains. We have never attributed a seizure to our oil, even at Havasu in 95'F air temp. water at 75 F, and rev'in 7600 ish,
did we ever seize. Hope this saves you some diagnostic time and money.