I got the amplifier out...I see zero signs of bad joints at all..
I am taking the one out of my 300TE and swapping it in as I know it works. You can see it seems there was a model update between 87 and 88:
Left is part #003 545 09 32 Date: 26/87
Right is part #003 545 05 32 Date: 20/88
Plug fits, so we'll see if it works. Will report back later with results.