Love my 301's.. .but they too are a bit picky about the bobbins I use, no freshly minted Chinese ones please.
It's funny you mention sergers that are acting up. Went to use mine today and it wouldn't form a stitch... upper looper is broken at the very tip.... sigh... have to track down a replacement. Moral of the story is I need to stop lending my sister my machines.... she always manages to break something but never say a word about it.