Does anyone know what size rivets I need to reinstall the endcap? What size drill should I use to drill out the old rivets?

3/16, but they're tough to drill out. Quicker way is to use cut-off grinder & cut off the 1" stopper portion, rounding the sharp corners as well. Pete

3/16, but they're tough to drill out. Quicker way is to use cut-off grinder & cut off the 1" stopper portion, rounding the sharp corners as well. Pete

Cut off the stopper on the end cap? And then the bolt keeps the car from coming off?

If you want to be more positive, back off the bolt & put another washer under bolt head. You may find that traveler does not pass the head of the slotted bolt, whereupon you will have to remove it & countersink a little further. Pete

Drilling out the rivets was easy. I used 3/16 by 1/4 inch rivets.

Don't let the rivets scare you, do it right.

Use a bit *slightly* smaller than 3/16 if you can (whatever you have - size isn't extremely critical), if the rivet starts spinning, angle the drill a little and let it spin while you drill away the head material. When the rivet head material is thin enough (you don't need to drill the head completely off), take a center punch and hammer and hit the center of the body of the rivet through the hole. Very easy. You don't want to use a 3/16 bit because if you're off center in the slightest, you don't want to risk enlarging the hole. If you do, this part isn't structural, so I wouldn't worry too much.

You may want to use a little silicone on the new rivets when installing for two reasons: to weatherproof and to keep a less-than-perfect rivet installation from any movement.

The above are techniques I learned as an aircraft mechanic. I can't tell you how many rivets I've replaced.

Like Pete, I needed to countersink the hole for the inner slotted bolt just a hair to allow clearance for the new car to get to the outer bolt (stop).

I used 3/16 x 5/8" but they were a little long. 1/2" long might be a little better.

The rivets are easy to drill out, just make sure you have a new bit and a drill with variable speeds. Use the drill on the slowest speed not the fastest. Running the drill on the fastest speed will dull the bit very quickly