Is there a product I can use to just spray into the alternator while it's running? WD40 maybe?

in the old days when I used to take them apart to replace brushes I remember there being a lot of soot around the brushes and coils and I am sure that's not helpful.

Thanks

 

NO!!!
If it ain't broke don't fix it!!!!
Alternators are maintenance free, they work until they dont then you replace them.