Had mine done on the 86 Olds Calais 2.5 [128,ooo miles] after getting it back from my brother. The sample I sent in was said to have indicators of coolant, but the head gasket had been changed before I bought it.
Blackstone said to sample it again in 1000 miles, as well as change it to be certain the contaminants were completely removed . I only have 100 miles or so on the fresh oil and filter as well as old coolant flush and replacement so CARJ's question is timely.
The odd thing is, I was suspicious of losing coolant back when I first owned the car from 92-99. It seemed to disappear at a slow rate. Parents drove it for six, then little bro for 11, before having to do a head gasket replacement some time in the past year or two.
Sample oil was very black, but the car will be going in for a total mechanical probe in the next couple of weeks.
Thanks for bringing up the question CARJ.