Fun weekend with trails

On Saturday morning, Willig and I went to Shelton to ride in another Poker Ride with Janis and Erin. I got too excited and couldn't sleep, then miscalculated the time I needed, so I got there an hour early. I was the second person there, and the first person was friends with the organizers.
I had to lunge Willig twice, and every time he saw horses leave on the trail he started thrashing around tied to the trailer. But once I got on him, he calmed down a lot. He even walked through big ol' puddles.
The trail was really fun. The long loop was "4 hours" but only took us 2, and there were awesome, incredible views of the Olympics. I'm going to try to figure out how you do one of the horse packing trips through the Olympics. Janis said she'd be interested. Willig started out pretty good (while Erin was passaging), but he either a) got tired and crabby, or b) got worked up when he saw horses ahead of us that we could never catch up to, or c) got worked up the short burst we cantered. I think b and Janis thinks c. But he proceeded to toss his head and sweat most of the last 1/3 of the ride.
It was a great experience for him though, and I got some local corn and won a couple things and got to see a Christmas tree farm and the Olympics.
Then Sunday, before the downpour started, Kevin and Mercury went on a trail ride with me and Willig. Mercury was his normal, placid, reliable self while Willig was one of those aggressive drivers who you are supposed to call the cops about when you see them on the interstate. He was riding Mercury's ass, then wanted to zoom around him and go slow, and flashing his headlights and beeping. He doesn't have any trail manners. Sam and a friend of hers were at the barn, so they hung out with him for a while and Kevin fixed some stuff in Willig's stall (the broken salt lick holder and restrung the wire I hang the jolly ball/Jimmy's ball on). They stayed inside because it was pouring most of the day, and then, becuase Kevin left his wallet in my locker, we got to go out and check on them a second time!
The bummer is that Sam left me a message today saying Mercury was lame so she didn't ride him. I'm starting to be pretty frustrated with this. He's either the gimpiest, most useless horse or something is going on. I don't know if maybe Sam is being extra cautious (but usually a trainer is there too), or if Mercury is acting up or what. It's hard for me to believe that after one trail ride he went lame. I'm planning on being out tomorrow and Wednesday, so I'll check him (and hopefully ride him) both days.
I really don't want to have to sell him, but I can't afford to board a horse who can't be ridden reliably. I don't really know what to do. He has a pretty easy, posh life. He has no reason to be going lame (if he is lame).