Just looking for a little help, I have a couple of old brown boots kegs, this kind;

With the co2 bulb injector lids;

Neither one of the kegs is holding maintaining pressure, I was wondering if anyone had any tips on how to overcome the issues?
I have spare taps I can use but I'm a bit stuck on what I need to replace the seals in the lid and the seal around the injector with? Or is it worthwhile getting a new lid or somehow replacing the injector?
Thanks very much in advance.