C25 is a general can bus error, do you know how to go in on the dash & get the E error code out that will be stored?

The later reach looms have extra plugs on, has it been connected up correctly in the reach carriage?

Has it got the short fused protection loom in plug 7 of the A5 card under the armrest?

Has the sideshift loom over the mast been checked for continuity / short circuit? you need 3 wires to the sideshift valve block.

Do you know the BT engineers name thats been looking at it? Id like a laugh lol