I don't know much about rc ground vehicles. Tony is the one for that, lol. However, I did do a "Google" search for your truck. It looks like a nice little truck. I wouldn't mind having something like that and the price seems reasonable. As far as the servo and the gears, it's rather unfortunate and very unhelpful that the website only lists the servo as a 3kg servo. I didn't see anything else that was more specific. However, I would imagine that you should be able to get replacement metal gears for your servo. I would check with your local hobby shop or pro shop. If you can, maybe pop that servo out of the truck and take it to the LHS for some Q and A.
Something else you might do, just for laughs, write down the measurements of that servo ( you know that it's a 3kg servo for trucks) and just browse around some of the websites and do some price searching on a metal geared servo that is the same size.
I sure do wish you the best!
