I have recently bought a second hand steel tank, engraving on top small lid says LPL. There are various japan and german made steel reels. 35 and 120 reels. My guess is it takes 7 35-mm reels, I was able to fit 3x120 and 1x135 reel. I calculated 200-cc for 135 and 400-cc for 120 reels. I am guessing these are quite standard so far. I haven't done any development in it yet, just cleaning it a bit and experimenting with steel reels.

It looks identical to Arista's steel tanks.

The problem is, the tank's lid is so tight. I sometimes need a screwdriver to force it. I looked at a few pictures on the internet it seems that these tanks don't have any rubber band on the lid, so I'm guessing that is ok with mine too.
There is no obvious bent neither on cap or the tank itself. The tank is not used for a few years in my opinion, it was just standing on the shelf.
Do you have similar experience with steel tanks with steel caps? Is there way to overcome it?