How do I replace right rear turn signal bulb?

Yup. Its the bulb. Check your owner's manual for exact location and bulbsizes. For my 2000 LeSabre I have to remove 7 nuts which removes the entire back panel - from inside the trunk. Not easy since you are looking up in the air with your head upside down and sideways. And you will need an extended length socket because it is up and in there. My local Ace Hardware guy tried different sockets until he found the one that would fit. My advice - buy extra bulbs - if the panel leaks any water or condensation, you will do this several times a year.

My front turn signal housing (2003 LeSabre) leaked a small amount of water which could be seen where it condensed on the lens. It probably got in through a drain hole or through brittle sealer between the lamp reflector and the lens. I had to replace the bulb holder because the contacts also were corroded - the glass part of the bulb separated from the metal contacts when I pulled it out of the bulb holder. I paid about $12-$13 on Amazon for the bulb holder. Then I used a small screwdriver to separate the lens from the reflector part of the housing, pulled out the hardened sealer / gasket, and replaced the sealer with silicone sealant like what is used for aquariums / glass. I let it cure for an hour as I kept pressure on the parts to make sure it sealed. Hopefully, I won't have to replace another bulb for another 9 years. NOTE: This had to be repeated for the other side.