Brake issue

This a very recent s/hand buy, maybe bought with this problem, unknown to me! Sadly as already mentioned brakes binding especially o/s front have checked brake caliper for relieve of "pedal pressure" and has that "small" return so not piston sticking, so replaced flex hose, no difference, so go to master cylinder release nuts drawn master cylinder forward approximately 1/8 inch and brake pressure seems to have subsided. As a matter of course can one remove scuttle panel where the master cylinder reservoir is mounted, so as to see/get at servo rod and see if there is any means of adjustment. The mention of brake light switch adjustment has made me curious! How does one go about checking the operation/adjustment? Have replaced o/s rear hub/brake sensor unit, freed off all brake pads in carriers and replaced b/pads, What concerns me is the ABS unit as you have mentioned. I thought there must be "ports and seals" and "one way valves operated by solenoids or "reed switches ", but if there was a problem here would a "fault code" show? Have read your extremely helpful "pointers" but could you advise on brake switch. Many thanks.

Vehicle listed above LX 124,000 miles reg WM06BTX.