Peter is absolutely right, and some come from impeccable sources too! A 7.62mm No.4 conversion I bought some years ago from a well-known gunsmith in Birmingham that used to be run by a dear old lady, came fitted with such a repro extractor. It was dimensionally incorrect and left too much space between the bolt face and the claw which allowed the empty case to drop out of grip as soon as the mouth cleared the chamber, causing ejection problems. The extractor had a distinct purple-ish tinge to the finish. Replacement by a genuine Enfield produced extractorfixed the problem completely.
Beware also of repro No.5 / Jungle carbine flash eliminators made from cast alloy.