Thermostat leak

[Retribution]

Hi guys,

My temperature failed to rise above cold a few weeks ago so I replaced the thermostat with one from halfrauds, all seemed ok easy job with no dramas. Then I discovered I had a leak from the thermostat housing. I then replaced the seal on the thermostat (which looked ok anyway) with a new one, again all seemed to be fine. Now i have a very slow low pressure leak, it only leaks when the engine isn't running , I have looked on wis and it doesn't state that you need to use any sealant or anything, I thought the seal on the thermostat should do the job. My next port of call is to buy a genuine SAAB thermostat just in case the seal is a little thicker??

Any ideas?