well I'm not really sure of the proportional valve ..as of what models its fitted to ..maybe mk6 without ABS..don't know.
and i would not want you buying a new master cylinder unless you were 100 percent sure.a definite symptom of a worn master cylinder would be pedal going all the way to the floor...that's if the rest of the system is in order.
An Abs system can be bled without forscan,
ONLY if there is no air in the ABS unit ..the trouble comes; if you let the master cylinder empty or you empty the system by disconnecting hoses etc ..and let air in ..then you need to "activate" ABS bleed mode on forscan ..this makes the abs unit operate on/off rapidly, it then operates motorised valves to purge the abs unit of air ...I've not done this act myself ..but heard
you need a couple of litres of brake fluid if you were to do this.
if you were fitting a new master cylinder ..then air would definitely end up in the ABS unit ( if fitted) there would be no avoiding it --
(sometimes)..and you would need to obtain forscan.
(sometimes) Take note how he purges master cylinder of air ..before connecting pipes to the system ...note he ignores instructions and does it his way ...that seams to work well.
https://www.youtube.com/watch?v=y_FjzrckA_8Another thing --- there are several choices of brake fluid these days ..you must make sure you don't mix the wrong ones with each other .
rules are you are aloud DOT 4 or DOT 5.1 preferably one or the other ...although they do mix.
or complete flush and renewals, if you use DOT 5 as this is
silicone brake fluid and
not comparable with the above DOT 4 or DOT 5.1
i think the factory put in 5.1 as standardall the best.mark