I used to use the service that went through Caterpiller dealers up here in Canada. The oil sample was sent to Cat SOS (scheduled oil samples/sampling)labs and the sample bottle and test was $25 or $28 back around 1998 or 2000 (Canadaian).
To be of real use, several tests over a period of time give trends on what is happening to the oil, engine etc. Good indications of problems starting to manifest themselves. A first time test can be very handy of course, but I think the real value of these tests is over time where results and repairs can compliment or indicate each other conditions.
FWIW, these tests pay for themselves the first time you have one done and thereafter. My experience has been mainly with bigger engines and power trains - but the theory is the same throughout the power ranges.
mariner
