Marflex changed hands and is now known as Sprayflex. I have a Marflex sprayer mounted on an old Chevy truck. It was our main sprayer for years; we still use it as a backup.
There really aren't any proprietary parts on one of these sprayers. The tank cradle and booms are welded steel and/or aluminum and any repairs will require cutting and welding. The hydraulics and sprayer components are common, off the shelf items.
The boom design is quite good, IMO, and the Sprayflex sprayers appear to use the same design.
Marflex seemed, to me, to be mostly a one man operation. I talked to the owner on the phone a couple of times regarding some modifications to the supports that held the booms in transport. The guy struck me as an eyeball engineer who was prone to making changes to various parts of his design on the fly. I've seen quite a few Marflex sprayers which are pretty much the same except that each of them had some minor tweaks to the way the booms folded or the combination of steel and aluminum parts on otherwise identical booms.
If the sprayer you're looking at appears to be in decent shape, I wouldn't be afraid of it. As I mentioned, all of the items that will need repair/replacement over time are off the shelf parts.
Mark