ZEV 4000LA/6000LA Speedometer Cable Drive Issue

Hi guy's and girls.
I have a ZEV 4000LA ( upgraded to 6000LA specs and beyond, 72v 100ah controller ), my problem is the speedometer cable keeps slipping out of the wheel drive unit unit, not fully out but enough to cause the speedo needle to jump and sound as though i have a lepricorn sitting on the front mudguard banging a spoon on a saucepan ( i kid you not ).
Every 3 to 4 days i have to remove the cable retaining screw and wrap adhesive aluminuim tape around the end of the cable where it enters the drive and it then works perfectly ( well no more banging ), the end that fits into the speedometer is nice and tight, its the end that fits into the drive unit that is the problem.
Without the tape i can move the cable from side to side about 1 or 2mm, it's as if the drive unit cable entry point is to large for the cable or the notch in the cable end is too big for the retaining screw in the drive unit causing the cable to slip back and partially engage.
So is there a replacement drive unit and cable that is readably available that i can bolt straight onto the scooter rather than going through ZEV ( shipping costs, VAT and Import Duty are a killer ).
The speedometer reading is so far out, ie GPS on phone and cycle analyst tell me i'm doing 31/32 Mph but Speedometer tells me i'm doing 50Mph / 80Kph ( no chance of getting done for speeding if i was to rely on the speedometer ).
Just a bit of history on the bike ( ZEV 4000LA ), i purchased it at the end of last year, it was one of a number of ZEV's that was purchased a few years ago by someone who was going to set up a dealership in the UK ( but he was declared bankrupt ) so had been in storage ( but regularly charged ), then sold on at auction, then sold to me.
I purchased the upgrade kit from ZEV ( new contoller 72v 85a and new voltage convertor ) plus a extra battery from the UK, all was fine untill just before i hit the 250Km mark then the original controller died ( due to one of the pcb tracks developing a break, killing a smd resistor and mosfet )
Not to worry as i had the upgrade kit, so battery box extended, new controller and voltage convertor fitted and a bit of testing later ( 2 hours to be precise ) and the new controller failed. So after lots of emails to Darius i returned the contoller and he sent me a replacement ( 72v 100a ) and since then everything has been fine, well almost everything, i'm 5 foot 2 and a bit inches short and 66 kilo's yet one a few weeks ago whilst putting the bike on the centre stand the kickdown part of the stand went down but the stand did not !, it did not just bend the kickdown part of the centre stand it peeled part of the metal away
Well thats about it, other than the problems i've had i have to say that it's a great scooter to ride.
So in ending this essay i'd like to sat thanks for taking the time to read it and any help in resolving the speedometer cable / drive unit would be great.
Cheer's Kieth. ( and yes Kieth is spelt correctly, child of the 60's with a weird mother ).