How can I fix my diplomat oven apl 3301 door not closing tight at top?

Hi, I have a diplomat APL 3301 oven that is bit loose at the top. My tenants are complaining that hot air is escaping. Had one handyman friend look at it and thought both hinges and seals looked ok. Wondering if it might be way to tighten it somehow or lift the hinges. Wondering also how normal it is for some air to be released at the top.
Any advice appreciated,
Thanks
Sam