There is already a perfectly good aircraft radar station up near blacksod in mayo. Why not stick a weather radar with it.
Secondly a delay in parts delivery in a airport with a DHL depot. You think it would be over night. Or perhaps even keep a few spares.
Aircraft radar sites are capable of having a weather feed off the setup, but theres a couple of factors...
Optimised frequencies in use for aircraft radar are usually L band for long range radars and S band for short range commercial radars.
Optimised weather radars are usually C,S and X band, depending on what you're trying to pick up.
So the only overlap is S band, which I doubt the radar in Mayo is, if it's more than likely covering the Atlantic.
To co-locate 2x frequencies on completely different bands on primary radar heads takes some expensive antenna engineering, along with the additional equipment required, you'll always have a tradeoff too, where the performace of both radars will never be as good a s a dedicated single radar head for each..... something that safety first industries like ATC will not go for. Also, sometimes it's just easier, from both a cost and "who looks after this" perspective to have 2 seperate equipment setups....
Depending on the age of the Selex radar, parts are becoming harder to come across, not knowing the exact model, it's hard to tell, but I've come across some other Selex issues where spares were made to order, as the equipment was pretty much end of support life.