Well, a season 4 episode airing tonight at 11:30 p.m.

When both Wanda and Davis sign up for piano lessons, the competitive drive comes out and makes things unpleasant for everyone. Brent and Oscar fight it out over the new air pump at Corner Gas, while Hank tries to help Lacey recover from her broken arm. Lacey's cast causes problems when everyone wants to sign it, except Karen.

Karen wont sign it because she had a traumatic "cast signing mishap" when she was 8 :lol:
Have they not shown this ep on WGN previously?

I am not sure.