200 Chassis alignment

[e2e]

Hi all
I came belatedly to the recent wheel alignment chat, as usual Phil's wisdom
is bloody mavelous.OK heres my problem;1990 200TQA,when I got it it pulled
to the left,it was under warranty so after a number of wheel alignments by
the (audi)dealer they agreed that it was tyre wear. A new set of tyres and
all seemed well I can take my hands off the wheel and the car goes
straight.So 35,000 km later the front tyres are shot and, more importantly,
someone told me that it "crabs" along the road slightly.
Before I go and get new tyres....
How can a bent car steer straight?
Do front tyres wear faster than rears?
Is replacement of two tyres a no-no?
Tyre rotation rules?
Chassis alignment and wheel alignment specs,where do I get them from?
-- 
Sam Clarkson