BBUS/ AMR 4974

My Defender alarm was playing up in the last couple of weeks... Whilst parked/ locked outside the house did a few blips on the horn for 24 hours before then setting itself off... horn plus siren, and the wife went nuts . A post mortem reveals that it seems to have been enough to blow the alarm fuse.... I'm guessing that the BBUS is shorting out, it is after all over 25 years old... I have read a few threads of people attempting to replace the embedded battery packs, didn't sound too successful... Official sources seem to be out of stock of the replacement part and its updates... Is there a best practice work around for replacing/over-hauling this unit?

Thanks in advance

Like you I have never read a thread where the bbus has been repaired or replaced with a new one.
Please report back if you have any success.