Iīd try to change the O-ring again. There are different types/materials that may solve the problem.
Unfortunatelly both tanks and ASA adapters may have small diferences in diameter which may cause leaks or prevent tanks to screw all the way in.
It may change. For example if you used a diferent tank with a wider valve, it may have widened or scratched the ASA adapter a bit. Maybe even damaged it. But I donīt think it is damaged since you used the rental tank with no problem.
Try your tank in others markers just in case. If the tanks are ok and it keeps leaking even screwing in all the way I see a few options:
- try a wider o-ring
- change the tank for a wider (valve) one (you should try it)
- replace the ASA adapter of the SP1
- if you like it, try a remote