Hi,
allow me to send you a wobbler, and set you into a spin.
You quote Mk1 and Mk2, then you should add a Mk3.
I don't know when the change-over of the boots took place but, IIRC it took place at Hoover.
The serial number may help to define if you have a Mk3. To decipher the serial n°. here is an example:
V50100545. Forget the V, the n° is set up as follows
5 01 00545
5 = 1985
01 = January
00545 = the 545th item from the line in Jan. 85
Hoover ceased production in Aug. 85, but I have 2 C5s with the serial n°. V510, this indicates they were produced in Nov. 85. These were probably produced by Adam Harper (at that time a Sinclair employee), who bought up all that was left over at Hoover.
I have 4 C5s that can be identified, two are pre Aug. 85, and two are post Aug. The pre Aug. models have Hoover on the stickers, but the post Aug. don't. I term the post Aug models Mk3s.
If it helps the Jan. and May models (the May model unused out of the box), have grey boots.