I would recomend using a product called Rislone. It is an oil additive that helps to SLOWLY remove depoisits in your engine. I use it in my vehicles to prevent any build ups. I would use it along with synthetic oil and change your oil every 2000 miles for about 18 months and then reinspect the engine. Even after you get the sludge down to a manageable amount keep using the Rislone on a regular basis and maintain the agressive oil change schedule. Good luck!
If you do decide to flush (i woudnt) i would drop the oil pan after words to make sure you do get everything out. Ive seen people flush older engines with no problems but have seen many folks have problems after flushing newer ones , flush at your own risk .