My Raze Buggy did a couple hundred barrel rolls with some end over end flips all in one crash today. Once I got the car right side up the steering was twitching & would only turn left unless I held the Radio servo right for a long time - once I let go it would always veer left.

I removed the arm from the servo and found that the Servo is twitching. The case looks like it's sealed so I'm assuming I can't do anything to fix it myself.

Is there an upgrade I can purchase down the road that won't need any other accessories or wires to the receiver? I'm new to this & trying to keep things as simple as possible. For now I'll be contacting Duratrax for a free replacement. They've been awesome about customer support so far...

Well from the way you are putting I would say you took out about half the teeth on on of the gears in side. Did this many times before I upgraded to Heavyer servos.

get a metal geared servo and problem is solved

Every servo I have ever owned even cheap ones you could take them apart. Best way to see if the gears are stripped. But I have to agree with 1/8racer get a good servo is the way to go.