I poked around the tuner and found what appear to be a damaged component. Luckily it's easy to unmount. While undoing the connections I noticed they were a little sloppy which makes me think it had been removed before.
Sure enough, there's a damaged 0.47 pF RF coupling cap. Not sure of the material but I'm guessing ceramic.
I seems the only modern replacement option is surface mount ceramic
http://www.mouser.com/Passive-Compon...scv7?P=1z0vqin