Since Shimmer is out of commission for the winter, my barn owner is letting me ride her horse while she's down south for the winter. I'd never even seen him before, but another boarder who knows him was there. I could NOT get him to pick up his left lead or even bend left. He'd give his head standing still both directions though. The lady was freaking about because she'd never seen him look so good. I asked her about it and she said they've never been able to get the left lead and are completely baffled. So barring any pain issues, any suggestions for getting him soft and picking up that left lead.

My first suspicion would be he’s sore somewhere. Usually a sore hock or foot will make one that way. 

If he’s not sore, make sure you’re not leaning to the inside or pulling his nose to the outside, which puts him out of balance to catch the correct lead. 

If the above doesn’t work, lope him counter canter him to the left (right lead, going to the left)  in a small circle until he would like to take the left lead. It may take a while and you’ll have to be tougher than he is ;-), but it will work.