If you mean the 4 inch floor flange, they sell replacement flanges to repair it if the old flange can be cut out.
It all depends on how bad the toilet elbow is, old lead elbows are almost impossible to repair and have cracks in the lead from people using steel snakes to clear the toilet plugs. The old flange can often be cut off the elbow if you can get clearance to saws all the old flange and use a new plastic repair adapter. If the flange is cast iron poured in concrete and it's old rusted away cast iron, it's going to be a bugger to repair.
Of course you never know how bad the flange is until you pull the toilet off the drain flange, then it's fix it right with a new wax seal. Not fixing a rusted metal flange will never seal up on the base wax seal and continue to weep.
If you mean the water inlet, they sell new O ring hoses for that, finger tight on the toilet valve and need an adjustable Cresent style or proper box end wrench at the 1/2 inch water feed shut off hose valve fitting.