Are there any lubes known to be OK on the plastic over the long term?
Yes, you can lube a polymer lower. There are a few different ways to do it, but the most common is to use a molybdenum disulfide-based lubricant. This will help to protect the polymer from wear and tear and make it easier for the bolt carrier group to move smoothly. You can also use a light coat of oil on the inside of the lower, but be sure to wipe it off afterward so that it doesn’t attract dirt and grime.
Another option is to use a silicon-based lubricant, which will provide a slippery surface that will help to reduce friction. However, this type of lubricant can attract dust and dirt, so it’s important to wipe it off after use.
Finally, you can also use a dry lubricant such as graphite or Teflon. These don’t provide as much protection as the other two options, but they will help to keep the bolt carrier group moving smoothly.
Whichever method you choose, be sure to apply the lubricant sparingly. Too much can cause more problems than it solves, so start with a small amount and work up from there if needed.