I was driving around 30mph when my engine suddenly shut off. Pulled off the road and tried to start it. Wouldn't even crank. Towed it home on a dolly, popped the valve cover and saw that an exhaust valve stem is bent and clear off the arm. Now, assuming the piston isn't beat to **** by the valve, I think the engine is worth saving. I've changed the head gasket before and I have all the tools for a valve replacement. Is it likely that when the stem bent it damaged the seal or guide as well? I'd hate to just change the valve and then have issues with what it moves in.

 

When you have it apart you will be able to see if the guide is bent/cracked or out of round, also you can check it with a good valve and see if there is any drag. There should be 0 drag between the valve stem and guide, with the seal removed.

They have service limits/clearances and they can be replaced easy enough with an oven/freezer and a valve guide hammer/press tool.