Aerosol cans often lose their propellant long before the contents go bad. This seems to be particularly true of lubricants, like WD-40.

You can see lots of videos and find web pages which describe how to re-pressurize an aerosol can using the air from an air compressor. While the original propellant was probably something other than air, and for some material air may degrade the material over time, that really doesn't matter because the alternative is to throw out the can.

This simple 3D-printed part provides a tight fit between the stem on the aerosol can and the nozzle of your air compressor. Because each can may have a different diameter stem, and because each air compressor nozzle is different, I produced this, with Fusion 360, using parameters. Thus, all you need to do is use the Fusion 360 paramater dialog to enter the dimensions of your stem and air compressor nozzle, export the STL, and print the part.

I used PETG in order to get more strength than PLA. I set infill to 100% because it makes the part stronger and also because the walls are thin enough that infill really doesn't help much.

One last point. When you use this, you should hold the can upside down so that, as you pressurize it, not too much stuff comes out. The stem inside the can goes to the bottom, so if you turn it upside down any air which escapes during the pressurization process won't carry too much of the can's contents out through this adapter, spilling all over you. (Recharging the can is sometimes a little messy.)

Creality

Ender 3

No

No

0.20

100%

I kept the fan off in order to increase layer adhesion.