For years, like 20 years I used WD-40 to clean my shotguns.  I strayed away from using it either because of influence from fellow shotgunners at the skeet range or fellow hunters telling me how it was not recommended for the newer weapons on the market today.  I adhered to the advice for one reason or another and purchased all the go to products for cleaning , but last season I started having some ejection problems with my Maxus which I thought was from powder residue gumming up the piston.  Long story short, I think my problem has been solved.  Went to the John Deere dealership and purchased their JD degreaser (spray can) which I use on the piston first to break down any powder residue and then back it up with the ole WD-40 and then blow it out good with my air compressor to dry it out very well.  What a job it does cleaning.  Read a lot about guys soaking the piston in gas(which I have done) but after 50-75 rounds fired it was dirtier with gas than my way? Does gas leave something behind I don't know about?  End result: Gun cycles better than ever with no further problems, Thanks old friend.