gasgasssser

hello everyone,this is my first post so forgive me if it not done right. i have a 1997 gasgas.today i noticed coolant leaking from a bolt holding the c/head on(h/gasket blown?),so i thought tthis was a good time to investigate a rattle which i have been putting off.After removing the head,i noticed that the piston has quite a lot of clearance in the bore,i measured the piston and it is almost ,35mm smaller than the bore.I`m giessing this is the cause of the rattle.Small end brgs and big ends are ok.Because i`m selling the bike in a few months i dont want to spend a fortune on a rebore, i`m guessing that`l cost about 200quid and i aint loaded.The bike is in good nick an runs really well and has bags of power.Any advice on whats the best option would be verry helpfull.