Engine replacement

I have a B&S 128M02 0115-f1-12020858 engine that's been problematic since new, thinking about replacing the engine vs. buying another new mower.

The mower itself is very good condition no more than 12-15 hours of use, is it worth replacing the engine or should I just buy yet another new mower?

If I do replace the engine, what B&S would have the same crankshaft diameter/length and crankcase bolt pattern?

If no more than fifteen hours should be under warranty, take it back, buy a Honda, Snapper, Toro, etc.