Thats the 1/18TH scale Ruckus. The 1/10TH scale came with either a 15T or 20T Dynamite brushed motor.
Welcome to the asylum, as i always say. More than likely, the motor just wore out. Brushed motors arent nearly as durable, or as long lasting as brushless motors, especially if they dont receive any maintenance. Typically, once the brushed motor goes, most ECX owners upgrade to brushless, but, if you want to stick with brushed, there are a ton of cheap-ish 9T (Arrma), 12T (Traxxas and several other companies), and 15T 540 and 550 motors that are a direct replacement. Even the original ECX brushed motor isnt that expensive. One thing to make sure of, if you go with a brushed motor, is to make sure you properly break it in. There are tons of tips on here, and videos on YouTube on how to do a brushed motor break in. If you decide to go brushless, your best bet would be HobbyWing, although, there are other cheaper alternatives available. It all depends on which way you go with it, but, any questions you have, you can always ask here, or, in most cases, a search will show someone has already answered it. If you do ask on here, and dont get an answer (very unlikely), there is a dedicated ECX Forum:
https://www.ecxforum.com/ as well.
Thats the Dynamite 15T. You would have to check Horizon Hobby to see if that motor is even available, if you decide to just do a stock replacement. If its not, any of the other motors i listed will work in it. A 9T or 12T will make it a bit faster, but, will need a different pinion.
I just realized you asked about upgrades. Sorry about that. There are a ton of ways you could upgrade it, from faster brushed motors, to brushless upgrades, of which, there are a lot of options. For the ECX 2WD 1/10TH stuff, i typically just pick up a Team Associated Reedy SC600BL ESC and 3300KV motor combo from either the DR10 drag car, or the SC10, or the Trophy Rat new off eBay. You can usually get them new for around $70. Another option is the Hobbywing WP-10BL60 paired with a 3300 or 3500KV 3650 motor. If you decide to go the HobbyWing route, and want something a bit more powerful, since the 10BL60 is only 60 amps, they also make a 120 amp ESC, but, for example, the 10BL120, as i recently learned, isnt waterproof, so, you really do have to research a bit to find one that is. The HobbyWing EZRun SC8 is waterproof though.