Shift assembly, Shift Lock

My 2nd gen Taco will shift out of park and into gear without depressing my brake. It will even do this without the key in the ignition. I find this to be a major issue because I'm worried about safety with my 2 little girls around. The dealer said they think it is the shifter assembly and the wanted to replace it for $1100 because I'm beyond the 36000 mile warranty. I feel like they should fix it for free. I'm at 59000 miles and I can't believe I'm having an issue like this. However, I can get the assembly on eBay for $100. Has anyone had this issue and is this component easy to replace? I can't find any videos that show how to change it out. Should the dealer have to do it?? Thanks Brian