I was just in a couple discussions referring to the use of which oil to use in situations similar to yours and would advise continuing the use of conventional oil unless you are having issues that may or may not be changed by changing to synthetics of synthetic blends and in some cases this change can make issues even worse. Also take into consideration the cost differences since synthetics are now many times more than conventional. I'm sticking with conventional oil in my engines that started with it but using synthetics in my newer things that require synthetic.