If you replace the starter remember you need an ignition protected one with an inboard petrol engine as fumes can and do build up in the engine bay and starters/alternators tend to spark internally during use.
If it's a separate solenoid just about any 12v one will do the trick, the easy test for the solenoid is to put a screwdriver across the big terminals and see if the engine spins over, HAVE A GOOD SNIFF FOR PETROL FUMES FIRST, THERE WILL BE BIG SPARKS!