Drake II Tank Lid Butts Up Against Wall Which is Causing Condensation Damage...PIC

[tesla]

I want to buy 2 more of these toilets but need to find a solution to this problem first. The tank lid has a small air vent in the back where the wall damage is (see pictured). Condensation stays in the tank with the exception of where it wicks out the air vent onto the wallpaper. This happened over a period of 2 years. I put some duct tape over the spot to provide some water resistance but the tape is soaked but appears to be doing the job for now (is duct tape water proof?). I'm assuming that its unwise to seal the air vent. My other toilets don't have this problem since the tank lids are rectangular, don't have an air gap and don't butt up against the wall. Any ideas?

Thanks, Barry