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.

There appears to be several new and used sram 10 speed rds on ebay

SRAM road is very incompatible with Shimano/Microshift.

Just get a 10 speed SRAM road RD. They aren't hard to source. QBP (the largest US parts distributor to independent bike shops) has Apex, Force, and Red in stock, as do Amazon and other consumer facing vendors. If you're in a pinch you can also use a 10 speed SRAM MTB derailleur or an 11 speed Road derailleur, which all share the same cable pull ratio, although doing so would be far from ideal.

The current Rival 22 rear derailleur still uses the same cable pull as the older 10 speed Rival rear derailleur. In fact, all of the SRAM 11 speed road rear derailleurs still use Exact Actuation and will work with your 10 speed SRAM road shifter.

No other major brand rear derailleur will work.

A few years ago I discovered that SRAM has different designations - a Rival road derailleur had "Exact Actuation" (I think) and the MTB derailleur had 1:1. I have an MTB commuter with 12-23T 8-speed rear and figured I'd put a road derailleur on with the Grip Shift. Nope - it would only shift 1/2 the cassette properly depending on barrel adjustment.

I just replaced my RD on my Trek from a mountain bike setup the previous owner had the bike shop setup to assist him with climbing and the cassette. I also changed out my RC when I did to my traditional preferred 11-32 with a SRAM Force RD wifli medium cage. I think I paid $108 for the RD which I was hoping to source a bit cheaper but I am a SRAM junkie and love the Force tier. I would say a Rival would be easy to source and Fleabay would be one of my looking points for sure.