A common problem with the right angle PCV breather adaptors on the 304 engines, is that they tend to come loose and will potentially fall out, due to only being a tapered fit. I came across this solution perusing a Facebook group and decided to do the modification myself. Two simple M5 grub screws tapped into the collars around the right angle adaptors. Could probably do with shorter grubs screws. But they where the only ones I had. I remember a while ago, a well known member on here (can't remember who), was asking for suggestions for keeping them in.