Welcome aboasrd Derek! With your side repeater, remove the lamp as you did to replace the bulb, disconnect the plug and spray some switch/contact cleaner into the end of the plug and on the contacts in the lamp holder. Refit, test.
You may have to repeat this several times before the combination of dis/re-connect and the switch cleaner cleans the oxidisation off the contacts.
If several attempts don't fix it, do similar with the bulb and holder but also worth checking the bulb actually works.