Anyone know the precise technical difference between Warm Up Regulators PN 034 133 403 (KV engined Coupe quattro) and PN 035 133 403C (WR engined ur-quattro)? Visually they are identical. Both have the diaphragm for full load enrichment. Are they interchangeable? If not, why not? Any assistance gratefully appreciated. Cheers Keith '87 WR