Recommended place to buy parts in UK? Specifically Duovalve

[frstep]

Despite Parrot of Doom's excellent guide, I failed to fix my duovalve - both sides intermittently stick and the valve itself looks fine. So where (if trying to avoid the stealers) is it best to find these sorts of gubbins?

And is it worth trying a s/h part?

(And should a list of useful suppliers be a FAQ/Sticky?)

Thanks,

 

[Blobcat]

Parts from the dealers can be good value (especially if you are a member of the MBOA as you can get a discount at almost all dealers with it). The parts are guaranteed to fit and Mercedes do upgrade parts for older models.