KZ1100 Cylinder Head o-ring question

I've finally got the funds to rebuild the top end on my KZ so I tore it down today and made a list of parts I need. I think I have everything figured out but I was wondering about the O rings used to seal the outside studs. Is it ok to buy four generic o rings for these or do I HAVE to have the OEM o rings. I ask because $9 a piece for o rings makes me cringe. I feel like I read a thread at one point in time where they mentioned using generic o rings with good results but I don't recall much else about the thread and searching o rings on the forums results in thousands of matches. Appreciate the help guys.

No eBay APP ID and/or Cert ID defined in Kunena configurationThere are photos of those O-rings on ebay and it appears that they are not a simple O-ring. The O-ring cross sections looks taller than it is wide. Hopefully someone here with more experience with these parts will chime in.

According to the specs on Z1E they are round but they are oval in thickness. 4mm x 2.5mm. That's why I'm not sure if a standard 2.5 or even a 3 mm will work the same. I'm not sure what kawasaki was trying to achieve with the Oval shape

Their special o-rings, don't skimp on those.