I checked my notes and found the following:
" Tektronix 466 Repair (October 2013):
466 early model, Timing circuit board A7, signal 'A' SWP START LEVEL to Q1002A
C1115 shorted (Tantal, 100µF/20V), replaced by AL-Electrolytic 220µF/35V "
Symptom of the 466 was no horizontal sweep, but vertical deflection was ok.
I chose the capacitor just by looking for a most close value fit in my new parts box.
The solder side of the A7 board is reachable only by dismantling.
As I did not plan to carry the scope around in a car (i.e. no shaking and rattling),
I made the repair process straightforward. The tantalum has been cut just at the body.
I soldered the capacitor to the remaining standoffs.