All vehicles were treated at Swindon Works.
In 1978 the three centre cars that were running in Class 117 sets (59478-80 in L433-5) were refurbished with the 117 power cars, and were the only members of the Class to receive the white/blue stripe "refurbished livery".
Details extracted from the vehicle record cars show that only three full sets would formally be "refurbished", these being B473 (December 1983), P464 (January 1984) and P471 (April 1984), all being released in blue/grey livery.
When the Class 117 refurbishment program ended in July 1980 attention turned to the Class 118s and they began to be released in blue/grey livery while unrefurbished. In January/February 1981 the two Class 117 centre cars that were running in Class 118 sets were refurbished, it seems odd to do the centre cars (59490/509) but not the power cars (51311/26 and 51313/28) although both the centre cars would be returned to Class 117 sets soon after.
One other curiosity is that the photograph album recording the refurbishments specifically mentions the 118s on the cover.
The table below shows the Works date and the livery applied for each vehicle. Information supplied by Eddie Knorn, extracted from the BR vehicle record cards.
Summary
Description
Diagrams
Refurbishment
Works Photographs
Numbering & Driving Inst.
Liveries
Operations
Non-Passenger Use
Images
Details about the preserved Class 118 vehicle can be found here.