ABS stuck on front right circuit

[Tobster]

Diagnosing why the car was pulling to the left under braking today I discovered that the front right wheel was not braking at all.

Very little brake fluid was coming through the brake hose after removing the caliper, so I tried removing the pipe at the ABS module to rule out ice in the brake pipe.

With a very big effort on the pedal, a small amount of very murky brake fluid comes out of the ABS unit where the front right caliper cirtcuit connects.

I think the valve in the ABS unit may be stuck shut but don't have the faintest idea how to fix this and am in two minds about disassembling the ABS unit. Can anyone advise?

[Tobster]

Found another question where a guy had resorted to smacking the nearest bolt on the ABS unit with a hammer.

I have no idea how or why, but this worked.

I don't think this is a permanent fix though, and the brakes on this car have been pretty awful since we got it in July (just changed the rear calipers recently also, and have done 2 complete fluid changes and had brown crap come through each time).

I'm taking it the ABS unit is full of crap, maybe that hid behind valves on each fluid change.

Can anyone enlighten me on this and suggest how to get the whole lot working properly?

[NickPicks]

Not sure about hitting an ABS unit with a hammer, but I guess it'll either fix it or make sure it's broken!

Can you get a new / exchange ABS unit for it?

I'm not sure about that age of car, but can the ABS pump be bled in basic settings using vag-com? Certainly on the later ones, you can use vag-com to make the pump operate and bleed itself.

[Tobster]

Don't have vag-com and don't currently have plans to get it as I've gone MTDI.

Could do with a refurbing guide, probably just wants some internals cleaning.

Another thing I'm concerned about is that the Audi 100/A6 manual states that the brake circuit can't run empty otherwise the ABS unit needs bleeding by VAG equipment. Replacing the unit would mean the same. Presumably vag-com lets you do the same thing?
Does anyone know if this is the case with the 80?