What did the top of the piston in question look like? Did it have a bunch of small 2-3mm circular dents in it? Check to make sure that the electrode from your plug isnt missing, check your piston wrist bearing to see if all the bearings are accounted for. You wanna make sure you have all of the schrapnel out of the bottom end before reassembly.
As the previous guys have said, often times when a kicker locks up, some assume its the kicker gear that just needs a bit of movement to free it up, when in fact, its usually the first sign of a piece of crap stuck under your crank between it and the bottom case.
Not sure what the guy is talking about, whos trying to sell you parts, but I have copied your quote from him, and I will send it to my old man (whos a die hard Brit, and a wicked builder) , for a 2nd opinion. There is no way on a stock head, that a piston can hit the spark plug, unless your plug is 3/4" too long? What plugs are you running?
Thats a wrist pin bearing by my finger.