I wanted to give an update. I ordered and received a new oil cooler part (which is the only way to get the plastic part I needed) and after reviewing how the little plastic part worked, I thought I might be able to use the old broken part. So I tried it and it worked. To remind everyone, the little plastic part that was broken was a pressure relief valve. It is there in case the filter get's so plugged that oil can't pass through it. So here is what I did:
I removed the oil filter and placed the spring inside the round plastic tube in the oil filter housing. I then placed the broken plastic part which was just the end with the nipple on it on top of the spring so both of them just layed in the tube. I then took the oil filter cartridge by itself, not attached to the oil cap, and slid it over making sure the plastic nipple aligned to fit inside the end of the filter. This seals the end of the oil filter cartridge. I then put the oil cap on and slowly turned it so I could hear when it snapped into place on the filter. I finished tightening it down and that was that.
However, I wanted a better solution than using the broken plastic part. I thought I could either design a replacement part or come up with an alternative using something already existing. One member on this forum actually sent me a design I could use to have a machine shop make parts. After some experimentation, I found that I could use a machine screw to accomplish the same function as the little plastic pressure relief valve. I think it is a #4 machine round head screw and about 1/2 inch long. The round machine screw is small enough to slide inside the spring and the head is big enough to fit inside the oil filter cartridge end to seal it. Because it is round, it tends to right itself and seat inside the filter to make a good seal.
I slid the screw threads inside the spring with the head facing upward. I then placed the spring (with the screw inside) into the round tube in the oil filter housing. I then put the oil filter cartridge and cap on the same way as described above. The round head allowed the screw to align correctly every time that I tried it to seal the end of the oil cartridge. Even though the spring and screw lays inside the tube to one side, it seems to be self aligning in the middle of the oil filter cartridge end hole.
Basically, this is a 10 cent solution for a cheap 10 cent plastic part that would cost you about $500 at the dealer to fix. I know some of you out there will say this is stupid and no way would you ever do this. I understand ... I am not a mechanical engineer, but this seems to work very well in my opinion.
I will post follow-ups after future oil changes to let you know if it continues to work as expected.