Cracked valve cover driver side 2004 F150
 

I just had my transmission rebuilt on my truck 103k over drive went out because snap ring failed. That cost me 2200 but that isn't the issue after picking my truck up from the shop, hadn't even left the parking lot I noticed my engine light was now on. They hooked it up to the computer it was a cam sensor code. They said it'd be fine to take home and bring back after Memorial Day weekend, upon getting home I noticed burning oil smell and a lot of oil on the inside of my engine compartment on driver side along with it leaking on the ground. After the weekend I took it back they couldn't find the leak for hours then pin pointed it to a cracked valve cover right behind the power steering hose. Idk what to do I know I have to replace the valve cover but I'm just worried as to what caused the valve cover to crack. I can't see the timing chain having enough slack to crack the valve cover unless the guide is broke. Any idea on how this could happen? thoughts on what to do and the approximate cost of this fix?? Is it easy enough that I can do my self?

the timing chain will break the valve cover mine jumped a tooth put hole in top of valve cover ran fine but leaked oil on ground and motor cause broken ten senor $ 1700 parts & lab.