air mass meters on mk4's can be cleaned up with carb cleaner as a temporary solution, but they're £75 from vw on an exchange basis, not £140 as you were quoted.
There are cheaper ways to turn up your boost but the ecu will only compensate the timing so far.. then your car goes bang. Anyone who recommends breaking open the ECU to solder in a new chip, rather than remapping by just plugging in to the obd port is a bit of a noddy.. i'd find yourself a new local garage if i were you 
Good points there and yes that £70 was on an exchange basis too, I forgot to mention that. This leads me to think that they must be repairable. I did try the carb cleaner on my Dad's but it didn't make any difference. What is it that actually fails with these MAF's as it obviously isn't simply a case of them getting dirty
