[Kev413]

Thanks guys,so far I haven't noticed this problem untill the van has been driven and the brakes applied fairly hard a couple of times IE:quik stops from highway speeds.The left front is the only one affected,all others are free.

The proportioning valve is a good theory,from what I remember the ABS pump does have 8 lines hooked up to it,which would mean 4 from the proportioning valve and 4 to the brakes.
EDIT:there are 6 lines to the ABS pump,2 from the master cylinder and 4 to the wheels,no proportioning valve found,it apparently uses the ABS as a proportioning valve.

Your right wiswind,the ABS should only release pressure,not apply it.

As far as the master cylinder or booster,I can't see how either of these would hold pressure on one wheel only,the master cylinder only has 2 lines coming off it,one for the front and one for the rear.

The brake fluid was fairly clean,a bit discolored,but not filthy,and no particles in it that I noticed.I did pressure bleed the system untill I got clear fluid from all wheels when I replaced the calipers by the way.

Thanks for the suggestion to post in flatratetech,going there now.