Folks, welcome a newbie. Looking at getting into an E30 M3 - i've got the choice of two, one has higher miles - almost 140k, and i've read around the traps that it's wise to change the time chain, sprockets and tensioner around this time. How much will the bits cost, how much will the shop charge me an can I do this myself (i have rebuit a 6 banger bimmer)