Today my 10 year old SRAM Rival 10 speed rear derailleur pulley cage broke away from the body. I'm not surprised - it has over 63,200 miles of use so I figure it served me well.

Anyway....finding a new one seems to be a little difficult.

My question: Are 10 speed rear derailleurs from other brands compatible? I've seen new Shimano and Microshift 10 speed derailleurs and was wondering.