Yes, remove the nipples and clean the threads good. Some may dissagree, but it will make removing them later a lot easier. I also put a little lube on them too.
my 1860 took 4 nipple wrenches, boiling, soaking in kroil, heating, beating, and lastly a trip to the Log Cabin to have Ozzie remove them. just a lesson in frustration.
Remove the nipples for cleaning, clean the threads, too. Put some teflon lube at the nipple threads. helps to prevent them baking in the threads. Reinstal.