There are positives and negatives regarding the use of an oil cooler. The positive is that in the summer, your oil will run a bit cooler if you ride for long straights at speed in hot climates. The downside is that in the winter (or cooler weather), your coil can take forever to warm up and you will get considerable condensation in your oil as a result and the oil will stay thicker for a longer period of time and this would be adverse to lubricating I think. To avoid this problem and take advantage of the positive, you can get an oil cooler with a thermostatically activated bypass. This will allow your oil to not run through the cooling fins in colder weather. The very best choices for this type oil cooler are those for Harleys (also air cooled) and they have a ton of them on
www.jpcycles.com - just choose one with a bypass. The Harley type oil coolers are also a bit better looking, in my opinion, than most of the metric oriented coolers.