Look at some of the internet part sellers and they will sell "Oil Filter" and "Oil Filter Kit". The Oil filter kit comes with the large O-ring for the filter cap and the Crush Washers for the Oil Pan Drain Plug.
For some reason the 2 Oil Filter Cap Stem O-rings do not normally come with the kit.
They are ordered separately but you end up with 2 that are the same size; which is what I have uesd. I have part of a quote that I copied from one of the members but do not know which thread it came from.
"For some reason the 2 Oil Filter Cap Stem O-rings do not normally come with the kit.First thing is to put the correct "O" rings on the filter head stem, (no, they are not the same, the lower one as installed is 6mm x 10mm, and the upper is 7mm x 11mm. Don't believe it, take a dial caliper and measure the stem)."
I do not always change the large cap O-ring or the drain plug washer if I am in a hurry to get the job overwith.
Also for some reason I have seen the price of the bare filter to be more than the Filter kit with the O-rings. In any event I always buy the Oil Filter Kit.
It is well worth your time do do some internet searches on the price of oil filters and buy several at a time which saves on the shipping cost. Some of the internet parts places have free UPS ground shipping if you spend more than a certain amount of money with some it is around $50 with others it is more.

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84 300D, 82 Volvo 244Gl Diesel