Lots of helpful information. Is there a difference between cleaning my D500 without a filter over the sensor compared to my D600 that has a filter over the sensor. Am I OK to do both of them and are they done differently?
No, they both have a covering, but the D500 is one layer and the D600 is two thin layers with a slight path change on the top layer and a compensating reverse deflection on the bottom layer that limits bandwidth to eliminate aliasing. You have no access to the sensor itself but the transparent cover is a rather hard material which on Moh scale is just a little harder than window glass, which is pretty hard.
So cleaning is not as dangerous to sensors as most think, we seldom think about damaging a mirror or plate glass window that is much more expensive to replace than a sensor. The problem with cleaning a sensor is working space and how fine of dirt can impact the results. With window glass, if it looks clean to the naked eye, it is. But with a sensor, dirt we can't see with an unaided eye can be seen in photos because we view images magnified many times so see spots, streaks, and specks easier.
I use methyl alcohol and add a tiny amount of glycol as a wetting agent. It is available from any chemical supply house for very little, even regent anhydrous methyl alcohol is only about $7 per 1000ml bottle. That will last a whole camera club about 5 years of cleaning daily. With the drier versions, there is less water so less of an issue with streaks. The glycol slows evaporation so it gives a few more seconds working before it dries. You can buy the same thing in tiny bottles in camera stores for 100 times as much per ml but its total composition is exactly the same. Probably the biggest rip-off in photography. You can get the wiping sticks from optical supply shops for supplies for maintaining optical equipment. I use small disposable sponges with a stick handle, about 10 for $2 and intended to clean quartz x-ray machine optical ports. The ones I get are about 3/4" wide and 1/4in thick.
That said little of my work is stopped down to deep depth of field range so seldom see spots. If you are shooting f/8-16 often you need to clean your sensor a lot more because you will see spots.
If you suspect dirt on the sensor and use Lightroom there is a great tool to find them. Turn on the Spot removal tool at the top right side in Develop mode. At the bottom edge of the main image viewing window, you will see an easily overlooked checkbox labeled Visualize Spots and then slide the little slider just to the right of the checkbox until you see spots and hazy area start to appear on the blacked out image. Then it is easy to delete them while in that mode.