In order to get the lock indicator the oven needs to run. I would try and repeat the procedure with disconnecting the control signal, installing the pullup and waiting for some time, whether the control signal comes on. Using that procedure the oven should turn on.
I would test the GPS receiver first, looking at it's monitoring output. It needs to receive and track some satellites. Everything depends on a GPS lock.
One could also check the frequency of the OCXO. The OCXO might require adjustment to bring its tuning range back to 10 MHz +/- some margin required for lock. Aging also affects electrolytic caps, especially those near hot ovens, resistors or semiconductors. This kind of maintainance is justified after 10 years. The unit will be much easier to fix than a rubidium standard.
Regards, Dieter