I thought somebody might benefit from these few pictures.
I personally hate doing any repairs on the Synchronar but when I finally get in the mood I try to do my best.
The transistor for the first left digit corroded due to battery leakage so I fitted a surface mount modern replacement NPN type.
I would prefer to install the original one but both my Synch carcases and Hanno's warehouse was out of stock ;)
It's a BC817 from Infineon technologies - just in case somebody would need one. You will need a BC807 PNP for the segment drivers.
You might need to file down the plastic SMD casing a fraction of a milimeter to make it fit within the height of the IC and reed switches.
Not to exceed the thickness of the main IC you will need to place the driver in the optimum spot on the board and solder thin wires and probably also use some masking tape.
One remaining task....is to fix the solar cell. Fortunately it broke just in between the panels so it's an easy soldering fix.
The potting gel sucked in the cell so much that it cracked while removing the module from the lexan and there was no other way or gap to pry the module upwards.
With another module I'll probably need to find a very thin but hard U-shaped wire to insert between the lexan and solar cell and remove the suction.