sure its every 60k or 5 years for cambelt mate. I know it is for audi's and they are vag so yeah. Generally its oil, fuel, air, sparks for a full service as you've already had a lube service. If you do your cambelt make sure you also change your waterpump as a precaution as they can go after you put a new belt on. The bearing isn't used to being in the position it was in before you took the belt off so when you put a new belt on it can potentially break and seize up which involves pretty much doing another cambelt so do it whilst you are there to save the hassel in the long run. Your sensor could be on its way out hence it being sproradic. Easy job to change, don't need to lube or anything just screw it in to about 20nm (nip it up with a ratchet) and it should be fine. If your problem persists maybe think about getting its faults read. Will be able to tell you if its the sensor or an open circuit but do it after changing your lambda. Don't know what oil you should be using. Refer to your handbook for reccomended oil.