E38 died or recoverable

hi all,

I've been contacted by one of my buddies whose car I worked on a year ago C6 Ls3 US model (we are in Germany, so we have also a different EU model here). I'd made tune fixes for a pro's mistake running 30deg + timing on an otherwise stock motor with headers.

Anyway, after sorting this and 1 year without issues on the track, he drove into the garage, the car died, and now it won't start, PCM no communication (with his data logger/ data logic). I live far enough away I've not visited before getting a handle on the issue.

Unfortunately, he's been running a lithium race battery that I think was glitchy. He put a spare PCM in, different year, different OS, just to see it the car comes to life - at least the ignition and things turn on now.

With the original PCM, 10 minutes before the interior lights come on, no fuel prime, nothing.

Is there something I can do, did the battery spike wipe out the tune and a full flash can save it? I don't want to travel over an hour to piug in and have no comms?

Further to this, despite searching the forum, I don't understand what replacement to tell him to get. What numbers do we match, physically printed on the PCM, serial number or something? does it report the OS already? OS is 12639270 from the last tune

We are in Germany, the car is a US spec,

thanks in advance