I had one of these same exact hoods a few years ago. I had no issue with rain but do keep it waxed often. Helps with beading up the water and protects the hood. They need it. I usually wax mine once a month.

Use a heat gun or even a hair dryer to heat up the glue along the edge and carefully pull the lens off the housing.

I would try the maf first. ive had this issue before as well and luckily thats the first thing i went for. put a new one on and ran fine after that.