Marconi 2945 Attenuator Relays

[atw60444]

 I'm looking for some help, please. I have a Communications Service monitor, Marconi 2945 which was giving low readings on Narrowband Power measurement and Spectrum Analyser, (about 35dB low).
The fault has cleared since taking the input attenuator out to test. It looked fine on a tracking generator up to 1.5GHz. But I'm sure the fault will return sooner or later.
After posting on my Twitter feed, a French Radio Amateur replied, to tell me that it would be the attenuator relays. I should replace all ten (across the two attenuators) with, specifically, Panasonic RK1-L2-5V-H23. These seem to be impossible to find. There are versions about with different suffixes, like H41 and H55 (I think, from memory). But there is no information on the data sheet explaining this suffix. The French gentleman is adamant that you need the correct part. But I'd like to understand the actual differences. I'm very grateful for his help, but Google translate isn't the most helpful thing with technical language.