Another dubious assumption:
"MoD's answer is that "this SI was withdrawn from use in 1995 and the details incorporated into he normal Chinook Maintenance Manual". So it looks as though the connectors remained and the SI just became part of normal servicing."
'Withdrawn' may be for any one of several restorative reasons, including a possible modification action, the details of which would be placed in the AMM.
Please keep this thread's discussion to 'speculation' and try to avoid 'wild' speculation.
Also:
Engine's missive that "Engineers should do it" implies blame on the shop floor when in reality they can only react (legally) to "Servicing Instructions" from design engineers/PT staff.
Clarification, not criticism.