Thanks everyone! 
The good new.. my compressor is working now. (don't want to think about WHY it wasn't)

 and fingers crossed it continues to.
The expensive news: I've decided to stick with the SLS despite the immediate expense! Strangy, i wish I'd read your post about an hour ago.. just ordered 2 bags from airbagman @ $295 each with free courier delivery (they'd want to be delivering it free with THAT much price difference!). 
So I can comfort myself that, despite the painful expense, I will have new bags today/tomorrow that are of a quality that may give me up to 10 years life the way I drive! 
 
Decided I couldn't risk burning out the compressor, and can't do without the wheels due to kids / school running around etc etc.
Found this great post and now have the confidence to put these suckers in myself. 
Land Rover Zone - View Single Post - Disco II Air suspension – the definitive guide
I found the complete article here to be really useful too: 
Disco II Air Suspension - the definitive guide
Gonna go buy a trolley jack now.. I can see I'll need it again. 
 
Cheers
Wil
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