ORIGINAL: nitro engine
you can reuse it but i did and within 2 weeks of soft running i had to replace it because it looked like it melted,i dont know if i put in wrong or what but i would not recommend it
if the head screws are torqued right, the head shim should last the life of the engine and then some. If it doesnt, me feeling is it was probably leaking causing it to run lean and consequently too hot. Most of the head shims I've encountered are .1-.2mm thick and don't take much to damage them. If everything is clean before reassembly and the screws are torqued right it should last a long time.