Hm, one last thing could be binding at the nut. My impression is that it's not likely the problem, but you could try lubricating the nut slots. There's products to buy or you could shave some graphite from a pencil lead.

Just trying to think of cheap things to try... I hate spending money :)

If you go purchasing tuners, a decent set can cost a fair bit. I put a set of Grover mini's on my last build and they were $50 US.

I'm not sure which sets might match exactly the screw holes of the Epi. I replaced tuners on my parts-caster with Grover 18:1 Rotomatics and had to fill the existing screw holes and drill new ones.