Hi @iceman2010
I had this a couple of years ago. If I recall correctly it's the one marked number 11 on the parts diagram. (That site is useful to keep as it has loads of parts diagrams)
I think that was the original part number, however I believe they changed it from black to red/orange at one point to improve it. I think, again from memory, the replacement part number is 91345-RDA-A01. I think that's the main one.
There is also another one on the other side which is 91370-SV4-000. I think I had both o-rings changed at the same time but have read elsewhere online that this second one might not need doing. My mechanic said for the extra cost of the o-ring it was worth just doing it and save more potential problems later.
When I did it, replacing just the o-rings wasn't enough, I also had to have the power steering fluid replaced as well.
Hope this helps