I have a tin of Homebase "one coat non-drip gloss" which is about twenty years old. It is solvent based, and has been stored indoors. It is that kind of paint which is a bit like a gel, and it says not to stir it before use. I opened it for the first time last night and found that there was a lot brownish oily liquid on top, much more that would be typical if it had been opened 20 years ago. So I stirred the paint, and did a test by painting over some gloss. This morning the test painting that I did seems to be okay. I am thinking to use it to paint a front door. The paint on the front door is an oil-based gloss in good condition. There are a couple of chips that will need primer and undercoat, but most of the door will just need a light sanding to make a key. Whilst it all seems to be okay to me, is there anything that I don't know? For example, will the paint flake and fall off after a few months or anything like that?