Pulsing rear brake is a common problem on XBR's. Usually caused because water has got between the cast alloy hub and the steel drum liner which rusts and distorts the liner. Problem is that the steel liner is quite thin so skimming the hub may not be an option unless distortion is quite small. It is possible to have the old liner removed, the drum skimmed and a new liner fitted but I imagine it won't be cheap. If you go for a new rear wheel make sure you aren't buying the same problem - good XBR rear wheels are scarce. Check the rear drum first, shoes and action. Also make sure the drum is centralised - put it on the main stand with the back wheel off the floor, loosen the brake off a bit, loosen the wheel spindle so you have a little movement then spin the rear wheel by hand and put the rear brake on and then , with the brake pedal still pressed on, tighten the spindle nut.
