Old, heavy grease can cake up the ballnut enough that the self levelling stuff can't get in there. IMO disassembling the ballnut and cleaning it and the balls/guides completely are vital to ensure smooth operation. If there's wear present it's most likely gonna be the balls/guides/nut as the gears themselves are pretty durable and have lash adjustment available. I used a cake decorating bag and a spatula to fill mine.
X-2 on disassemble and clean up. This way you can inspect it properly. If your pour something in to clean it theres nothing to say you got all the old crud out.
Mark
