light gun games need crt, an LCD won't do ,actually some of the Sega ones maybe as they run of sensors , repair can be tricky but is possible for most CRTs, replacements are about but can be expensive and risky to ship.
Depending on the games the mb or myriad of other boards themselves could also be costly.
I have sent two monitor chassis (just the mainboard basically not the tube) to the UK, there are a few guys on UKVAC that fix them.
Also a few guys in Ireland that do it but "Gunblade" has all the parts already.
Yeah I've had Grantspain fix my Pony's chassis (it crapped out on me after a year of use)
Myrddin was also nice enough a few years ago to do a cap kit on my SNK cab.
The images on both monitors is now super bright and crisp, should be going for many years to come.
Removing the chassis is actually a really simple process, I took a few snaps along the way with my phone just to remind me where cables reconnected.
The only 'scary' bit is discharging the monitor. There are loads of guides online, it's nothing too technical, just a bit unnerving the first time you do it.
Actually, now that I mention it, it was Enternow, he was a sound lad.
All Myrddin did was close the Sega forum