so had a awful experience with a garage that i recently used and got a service done and a few other bits on bobs. he never wrote on the receipt what grade oil he used but the make was millers what if it ever needs topping up ? when i go on millers they say i should use 0w 40 but not sure if he used that am i better off just draining the oil this weekend and changing it or if it ever needs topping up just use 0w 40?. if so what oil would people recommend. i am quite competent with a spanner i just took it to the garage to save my time and help a local business which now has backfired horribly