I have a 97 Z3 with 230K plus miles. The engine pulled strong when purchased, but with an inordinate amount of top end valve train noise. I believe this was due in large part to sticky lifters and severe camshaft / camshaft journal scoring. I believe this started many miles ago due to negligent oil servicing and not replacing the valve cover gaskets. In particular, there is a rubber nipple on the head that transfers oil to the upper cover camshaft oil lines that deposit oil to the camshafts. That nipple was hard as a rock and there is no way that the oil could transfer at 100%. Not to mention the fact that the valve cover assembly needed extensive cleaning with particular attention paid to cleaning the small orifices on the oil tubes that are directly above the camshafts. I did not want to use the original head, so I purchased a used replacement. I polished the camshaft journals and cams by hand, lapped all of the valves, installed new valve stem seals and cleaned all of the coolant and oil passages. I did not replace the lifters, but did clean and polish them for re-use (it took some effort to remove them). The head was reassembled and installed with copious amounts of engine assy. lube. I did note that cylinders 2 and 3 at TDC looked brand new after removing the head! All of the cylinder cross hatching is perfect. Not bad for a 230K plus motor! The motor runs great, super quiet valve train now and good oil pressure. The combination of poor oil servicing, lack of periodic maintenance (valve cover seals) led to oil blockage causing camshaft journal / camshaft wear and stuck lifters. Bottom line, keep that oil clean and these engines should run forever! (photos taken of the original damaged E4 and E5 camshaft / camshaft journals)