I had this happen also.
Jack the deck and place it onto some wood blocks, to take weight off the links. Replace BOTH of those bolts, on both sides, as the other one will fail too.
Buy yourself two suitable grade 8 bolts, 6 matching nuts, 4 wide washers and locking washers.
Remove that bolt completely.
Place your bolt in half way, so that its end is exposed, and roll a nut onto it. this will be your backup nut.
Roll second nut on, then locking washer, then regular flat washer.
Leave enough bolt exposed to go through the links and come out on the inside, so that you can place wide washer>locking washer> nut onto it.
You will need to play with nuts on the bolt positions to find proper length.
Tighten two inside nuts on the links. Then tighten back up nut on the nut. If you want to, add 2nd back up nut on the inside too. Won't hurt. It looks like crap - HOLDS like a bulldog. If you need link to move, not jammed, slide a washer between links. It'll act as bearing.