Okay things have settled a little with this since I'd removed the engine radiator cabling as I knew the module was leaking to earth and did ohms test to prove it (P0691). With cable disconnected, no P0691 code and the battery is staying around 12.8 at night and starting with glow plugs of 12.2 ish instead of 11 or sometimes 10.5 for a short second or two till glow plugs go out. I've still got P0380 being posted but she starts so well I might just replace the relay and not bother with the nightmare glow plugs.
Replacement rad and module on way...should have her sorted soon!
- jeebowhite likes this