BMW Repair: Engine 525ia bmw, blown head gasket, piston rings

Question
I bought 93 525IA BMW Over 100k miles w/ Blown head gasket to off head #1 piston has two half inch cracks on piston. Is it best to replace one or all 6 w/ rings or just one w/ rings. And piston has burr on edge. I would to have ur insight on this car.Ibought for my mother am I wasteing my money on this beamer or what.  THANK YOU FOR YOUR TIME.  

Answer
Hello Andre,
Have you verified that your problem is only the piston with the 2 half inch cracks? Is the bore of the piston still ok
with no scrapes? But I doubt that the bore is still good
since the piston has a burr on the edge probably from hitting the cylinder walls. You should also have the cylinder head checked for cracks and warping.
The proper way of course is to replace all pistons and put in new rings.But why throw good money after bad? If you can buy one piston of the right size (including piston rings) from a junkshop then do it. Once the car is running, do a compression test and if there is loose compression or too much difference (like 20 psi) between two adjoining pistons
then sell it and buy another one.