The oil in the tank drains down into the sump over a period of inactivity, it's an S&S X-Wedge problem and some engines are worse for this than others. If you haven't started the engine for a long time it is well worth checking the oil level in the tank, if it is down DO NOT TOP IT UP. If the level is down more than an inch from it's normal level, remove the drain plug in the engine case sump (Allen head) and drain the oil into a clean container. Refit the plug and return the oil to the tank. Start the engine and run it for at least a few minutes. Turn it off and let it settle for a couple of minutes, check the oil level and replenish if required.
I would think that if your cam belt is cleaned off it will be fine. The crankcase vent system burns off the fumes and puts a slight negative pressure in the system so that seals will not leak so easily. It has a calibrated 0.1" orifice and really doesn't need any modifications to improve it. It works fine as long as the sump isn't full of oil when you start it.
One other problem that can occur and is easy to check is a blockage to the tank vent line, the thinner hose from the top of the tank to the upper of the three hoses that connect to the front, lower RH side of the engine. Disconnect both ends and blow through the line occasionally (put a bottle over the other end to catch the "mayonnaise"). This will be more prone to blockage if you use the car in cold conditions a lot, it needs to get hot to vaporise the condensed water out of the oil system. If this line blocks it can lead to oil tank ruptures and leaks, particularly with the early dipstick type tanks.
If you are a member of the MTWC there should be an article about the M3W oil system and it's problems in the next issue of the Bulletin magazine.
