I have also seen flux gum up the diaphragm beyond the tube. I have cleaned the diaphragm twice and each time I clean it the tool behaves just like new. It is a small job to clean it but I recommend doing that periodically.

I can attest to this. I generally use the 1.0mm tip and pretty much only use the 1.6mm tip for the 0.156" connector pins, bridge rectifiers and snap-in radial capacitors.

Don't forget to drill out the nozzles as well to keep them clear of debris.

I have the FR-300 (now obsolete) and when I clean it I clean it. I take it apart all the way to the diaphragm. I've seen bits of solder and flux back there. The flux is sticky and can gum up things. When it's all cleaned out it's like a brand new tool.

Note to 808 users that the heater (A1234) is discontinued. A good friend of mine had the 808 and used it for years, until the heater broke and he was unable to get a replacement. He now has a 301.

It might be comfortable or natural to put the board flat on the bench and "fight gravity" rather "let gravity help". There is an intermediate to this. You can "neutralize" gravity by standing the board on its side (vertical) and performing the de-solder operation "horizontally". By doing it this way, you are neither fighting gravity or getting a gravity assist. It is (mostly but not entirely) neutralized.

This takes some getting used to but you can train yourself to do this.

If you know you are going to discard the component that is to be removed, you can cut the component out and then remove the remaining parts. An example of this is to cut all the IC legs (closest to the body to provide the maximum amount of remaining leg to grab) and then individually remove each leg. This makes a clean removal much easier as you can manipulate each leg individually rather than the IC as a whole. Another way to cleanly remove a whole IC is to use hot air but that is beyond the scope of this thread that is about a vacuum de-soldering tool.