Having grown tired of fumbling around with my attempts to homebrew my own repeater, I've just ordered a shiny new Bridgecom BCR-40U (400-470 MHz) UHF Repeater, complete with a properly tuned duplexer and the programming kit. It should be here within a week or less.
I had my handy man out today taking advantage of the warmer weather and low winds to do some maintenance on my roof mounted antennas. One dual-band antenna's top section was lost several years ago (the VHF part), so I had him swap the coax over to another dual band that I'd put up some years ago as a backup.
Hopefully all I'll need for the spring is to buy some 1/4" Superflex heliax and a better antenna for the repeater.
I also made contact with another ham in the area who's kindly offered to (re)tune my existing duplexer.