How does oil get in the coolant and vice versa other than ring blow by? It seems to me a small head gasket leak could quickly foul a plug (in this case about 100 miles) and cause a misfire code before there was noticeable oil in the coolant or coolant in the oil. When I lost the HG in my 80, I...
Hmmmm........so far this sequence bugs me. A perfectly running LC starts to have problems shortly after a dealer service, then after another dealer service and repair fails with a problem that is almost unheard of in the 5.7L engine. Makes me wonder if the initial problem was just a bad coil...