£6.60 should do the trick. You will get a sample bottle and tube, questionaire and return post and packaging. The result comes in about a week. Don't make the mistake of buying the kit from the guy who advertises in PBO. For £30.00 the only added value is a (single) rubber glove and a bit of Tippex over the above lab details (I am reliably informed that Finnings bought a 'PBO' kit, submitted a sample, had it sent back to them for analysis, despatched the results, and received them sometime later, complete with Tippex!).
Finnings are a Catterpillar dealer, test the RNLI samples and those from many haulage fleets and plant engines the size of a house, a director is a yachtsman I understand.
It is recommended to take a baseline sample after about 30 mins on the new oil, then a further sample at oil change time.
The lab will advise on a whole range of issues based on contaminents including:
Over fuelling
Poor combustion
Internal leaks
Poor filtration (air intake)
Bearing wear
Cylinder wear
Poor compression
Valve wear
etc etc etc.
You can't buy that much in the chandlers for under a tenner can you!