Hi Didier!
Could you please check the 10Mz reference clock? The errors your system show are all related to the clocks. but as the MOD also failed, it should be before the 437MHz SAW module in the HF output stage container. But may be, just a RF cable fell off in the bottom container while you where working on the top part.
However, finding one leaking cap is only a friendly reminder of the hardware that there are 372 other caps are eager to fail as soon as possible. So please check for discoloration around the SMD electrolytics on the other boards. And I want to forward an important advise from a certified Wavetec Service Engineer: The THT electrolytics fail too, and they like to fail hot! With the Amps the power supplies can deliver a shorting cap can burst into flames. So check these too.
I will start restoration of another four 4031 in the next few month, hopefully I can setup a new parts list at digikey for all to share. The ones I have a totally obsolete due to the parts shortages over the past two years.
All the best for 2023
Ulrich DC3AX / AG1U
OE3UPR / DC3AX