Unless someone added them (possible, but not very common), Spitfires don't have valve stem seals. I'm with Tom; rings could be stuck, or they could be bad. See if you can free them via the MMO as Tom suggests, and then maybe give the engine a bit of time to 'bed in' again after that long rest. Possibly, things will work out; more likely, you're looking at some level of overhaul.