Duraterm GP's w/ old relay?

[Maroon 300D]

Howdy, folks. I'm changing my GP's for the first time and while 99% of my questions have been answered by other threads, I have a couple more.

I don't have a Duraterm relay (it's a Mercedes relay, probably the original) but I did get Duraterm plugs. This won't be a problem, will it? I'm about 95% sure it wouldn't be but that other 5% is nagging at me...

Also, the old plugs were 11.5 volts, not 11 as Mercedes specifies for my car. The PO said he had just had the plugs changed when I bought it, which was January. Could this voltage discrepency have caused the short life of these plugs? I have taken two of them out so far and they do look fairly new, like the PO was telling the truth. The parts number for these plugs ended on '001.' I think the new ones end in '039.'

Also, this job was truly a PITA until I bought a 12 mm ratcheting wrench yesterday. If you have never done this job before, I would say one of these wrenches is a must.