On the SR (SWD) Clapham Yard had it's own light maintenance facility, a three road brick built shed, demolished I believe around the same time the (SR based) LH trains finished, so about 1980 ish, when the paper trains ceased to run. Clapham was an ideal location as virtually all SR(SW) based LH stock rotated through there. Not sure how much work was carried out there in later years, probably brake blocks/gear, any other minor defects that didn't effect the actual running of a vehicle. Can't find any evidence in the limited number of CWN's I have of any booked works trips, many vehicles for Eastleigh works I suggest were likely tripped via other services, in an age when there was ample scope to move vehicles via service trains. If anything (EMU) needed 'skating' it would have been arranged by Control on a one off basis as well I would have thought?
The WR 9 Sets (LA based) still visited Clapham after that of course, but only for stabling. At least one of the diagrams rotated through Eastleigh every night, possibly two(?), so anything that became red carded could be detached there, otherwise left to run until back at Laira.