Had the same issue with the drawer guide ends on my old Max-Lite. The ones that hadn't already broken were about to. That was one of the first things I checked non the new trailer and I believe they are metal.
When you do decide to replace them, find a bulk package of 20 to buy... and make sure they are the heavier-duty household quality. Those should last a while. I swear the OEM ones in my old trailer were made from the same material as those biodegradable, disposable forks...
The other challenge you may encounter is, when installing the new ends, you may find that it will be difficult to get the screws to take hold in the existing holes. You may have to fill the holes with something and then screw the new ends in. And, to make it an even more enjoyable job... getting both arms/hands into those spaces is a real treat!!
Have fun. :-)