Yea, the lid design does make it hard to get to the O-ring. I haven't had the nerve to remove it yet but I do clean it with a cloth and work some lube onto it with a Q-tip. Be sure to use silicone lube meant for this purpose.

Try the shaving cream on the plumbing joints as well. Perhaps it's tight under pressure but not under vacuum.

Good luck, let us know how it goes. Suction leaks are tough.