Interested in a spare? Postage cost only.... not much use to me.My 2008 has the round section 'o' ring.
Hedditch
There is no difference in the sealing of the filter housing using the square 0-ring or the round o-ring. They both will seal. Round o-rings are used in hydraulic system for umpteen years as the square type up to 3000 psi. Square o-rings are usually used on applications where there is a bit of debris present on the sealing surface. Round o-rings are usually used in a more universal application, with ease of assembly, service comes into play. Housing tolerances will also come into play. The pressure is low enough in engine where a softer seal will seal better
Materials will also make a difference. Buna, viton, carbon, polyurethane, silicon, etc...
I guess, what I am trying to say is that, if the filter housing and associated seal is used in the filter receptacle, then it will seal exactly the same.