I'd try replacing the pickup rollers and separation pad. Its likely the issue the no-longer available kit fixed.
This kit appears to be NLA too: http://www.printerworks.com/Catalogs/RollerKits/LX-RK_RollerKit.html
Parts are going to be hard to come by for these older units, they weren't very reliable to begin with as LX printers tended to blow up power supplies on a regular basis (that "dead fish" smell they make is something you'll never forget!). The cassette was an optional unit on these machines, stock configurations used the MF tray by default. It looks messy, but that is how HP and Apple sold them new.
This kit appears to be NLA too: http://www.printerworks.com/Catalogs/RollerKits/LX-RK_RollerKit.html
Parts are going to be hard to come by for these older units, they weren't very reliable to begin with as LX printers tended to blow up power supplies on a regular basis (that "dead fish" smell they make is something you'll never forget!). The cassette was an optional unit on these machines, stock configurations used the MF tray by default. It looks messy, but that is how HP and Apple sold them new.