Dear Graham,
Going back to basics I am certain that in 1946 the British Army still employed WW2 style markings, so apart from a vehicle number beginning with M, the Jeep would have carried the Divisional Marking, so a Y for the 5th Infantry Division but in 1946 the Div sign was changed to a white Y on a black circle, according to Howard Cole's book on British & Commonwealth Formation Badges. This replaced the Y on a Khaki Square marking.
Next is the arm of service marking (assuming the WW2 / NW Europe rules continued). An Inf Div in NW Europe would have had Red Square for the Senior Brigade, Green for the next Bde and Brown for the Junior Bde.
With three Battalions per Brigade the senior Bde used 81 for HQ, then 55, 56 and 57 for each Battalion in seniority, on a Red Square, the next Bde used 87 for HQ, then 60, 61 and 62 on a Green Square and the Junior Bde used 94 for HQ then 67,68 and 69 on a Brown Square.
It was only in 1948 that there was a reduction in regular Regiments and Brigades, so I assume in 1946 the make up was the same as WW2 more or less.
I could not locate the Bde that 2RWK were in during 1946, as this will determine the AoS marking and colour of the Square, either red, Green or Brown.
Further study is to see in DBG colour was in use in 1946 especially for Jeep rebuilds.
Also in post war period the British Army changed the vehicle registrations, so you Jeep may have ended up with a registration like Ashley's Jeep; 46 YJ 36 in place of the M number.
Someone on here will know about DBG and new registration introduction dates.