Hi ppea
Your original post and your photos made me curious of course, as I have the same air cleaner on my GX 390 engine as you.
Our filters are of the oil-bath type, and what I noticed on your photos, is that there are hardly any traces of oil to be seen. Could it be that there is way to little oil in the air cleaner case to make the cleaner work properly?
I just removed my air cleaner and made this photo for comparison:
As you can see, there are clear evidence of oil allover, and the filter seems to hold back debris as intended. I will of course need to clean it, and fill it up with new oil.
Here ia a photo of the air cleaner case, and also here debris has been filtered out:
When I clean it, I usually fill it up with new oil so the oil is flush with the horizontal „fins“ at the bottom of the air cleaner case. That has worked fine now for the almost 400 hours that I have used my tractor over the last 13 years.
A low oil level might not explain why parts of the steel wool is missing in your filter, but in your case I would replace the steel wool filter, and perhaps check the oil level more frequently in the future. If you don’t find the missing steel wool in the air cleaner case, there certainly is a risk that it has entered the engine, and that can’t be good
I hope that you haven’t had any problems with your engine due to this, and that with a new filter you will be up and running again soon
Best regards
Jens