Maintenance on the XCR for me was mostly preventative and a couple of broken parts. Maintenance was simply tightening and lock tilting parts. The BHO broke a couple of times.
The Virtus has been faultless so far and unlike the MCX doesn’t destroy AR triggers without a bridge so mine has the Geissele SD3G fitted and that makes it a lot of fun. The only thing I miss vs the XCR is the bolt release. That works the same as the AR so it’s no big deal. If you need spare call Sig directly and over t8me spares will emerge.