3mm rubber seal

hi all
I have a small hatch on the back of the camper for external bbq point.
there is a 3mm round rubber seal in groove in the the door which has perished and is letting in rain.it was leaking in the top but not out the bottom so the space was full of water and the water was getting in where the gas line entered the camper.i ended taking out the seal because it was in bits

I chanced ordering 3 mm o ring rubber on the net but the rubber is too firm and probably won't compress at all.the door plastic is quite brittle and I am scared I will break it.

any suggestions please

thanks john

the thing is that I don't think its a gas related part.
I also have an external shower point that is in the exact same type of plastic enclosure.
its like the toilet cassette door only its about 4" x 2" size wise

Will try to upload one tomorrow.

Thanks phil

Fair play to you. i think http://www.sealsdirect.co.uk have exactly what i need

cheers

Seals Direct are a very good crows to deal with and very helpful and know their stuff.

Ken, I've got the new iPad Pro so I blame it.