Just purchased a 2005 ltz 400 and when doing oil change everything seemed fine but when i pulled oil filter after draining oil the tiny o'ring gasket on backside of filter was not there and was wondering if i can get away without using it like the previous owner should it be bought and used as repair manual states? The one o'ring on oil filter cover is still in good shape, if anyone knows part num# or size of smaller o'ring or if even needed would be greatly appriciated. Thx. R.J.