I had this on my original MS. It went intermittent where the head unit plugs into the battery. A gentle wiggle about on the worktop isolated it.
I tried the Maplin connectors but they will no longer be ‘weatherproof’ and come apart easier then the MS ones out on the trail. You also have to do a fiddly solder in the plug and socket (live wires in the battery side) and the strain relief isnt great (the grommet / throat bit seems too big) so it didnt last long.
Next I got a MS ‘extension’ lead from DX (I also saw them for sale online in the UK recently). I cut this in half to use both sides as ‘pigtails'(if that’s the right term?). Then cut the original cables short of the dodgy connectors (for the battery side you’ll need to cut the inner + and – separatly or you’ll short the battery). Some easy wire to wire soldering, heatshrink and self amalgamating tape: job done and still working.
Edit: one of these: ebay extension
Take care if / when soldering the battery side cable. It’s live remember.