I am looking for help of any kind. I have a Volvo engine that has a piston sleeve with a crack causing coolant and oil to mix in the engine per the mechanic. The piston with the cracked sleeve looks like it has rust around it while all of the other pistons look brand new. Should I overhaul the engine or just fix the one piston and keep going. The truck has 535K miles on it. Also if I decide to do an overhaul the parts are not available right now would anyone suggest using after-market parts? There is a company that claims to sell overhaul engine parts that are up to OEM standards (ATL Diesel out of TEXAS). Please do advise any input would be helpful.