Ray,
You asked about removing door hinges.  I too have had the same 
problem - I used like you have an impact driver and a big big hammer 
- three came away - this was with olenty of persuasion with WD40 
(lubricant) the other one I stripped - so in desperation I drilled & 
used a stud extractor (at a slight angle cause of the seal rail) - this
 worked better than I thought - and it 
did'nt affect the threads at all. All then to do is to buy some new 
countersunk screws - and some plastic 'caps' to go over the srews - 
and Bob's ya Uncle (as they say in England!)
It's worked for me - so it should work on your IMHO

Cheers
Ricky
1991 Mexi-Bug
1967 Split Camper
1995 Overdraft         

"Turn On, Tune In, Chill Out"