Mine doesnt have that big rubber piece. Mine came from KDI

 

Would someone be willing to take a picture of theirs?

I'm going to post the tear down as well as the rebuild, as I discovered in tearing this one apart that the Previous Owner had reassembled it incorrectly. So here you are, and perhaps a moderator might want to turn this into a tutorial?
Remove the lid by removing the front E-clip and hinge pin, and also remove the latch E-clip and hinge pin, exposing the latch spring within. These E-clips are still available, and though I don't here, I suggest replacing them.
 
Remove the main/larger E-clip.
 
Here's where the PO screwed up. The large rubber seal appears to be on the correct plate, but actually, it's not.
 
It's on the sandwiched plate. You can also see the broken post seal inside the spring on the underside of the cap.
 

At any rate, remove that old large seal.
 
When you take it apart, take pictures of how it goes back together. In this next picture, I'm stacking them the way they came out.
 
The small round seal goes on the small disk inside the sandwich.
 
And really, I'm not sure the PO has used the correct seal here, as you will see later. Again, I have stacked the parts in the correct order when I take the pic.
 

These metal parts I'll soak in Berryman's for a while, and I'll clean them with a brass brush and metal polish, and follow that up with soap and water.
 
These will just get the metal polish and soap and water.
 
Cleaned up. The pic makes the underside of the top look filthy, but it is clean and shiny as you will see in a later pic.
 

Installing the small round seal is tricky. You must keep the vent holes always 180 degrees opposite one another. There are a couple of helpers for that.
 
With the vent holes opposite one another, look inside the seal, and you will see the lumps that need to align with the cutouts on the metal plate. Here you can see one.
 
Here in this pic you can see both nubs in their slots, one on either side of the screwdriver bit.
 
In this pic, the seal is on the correct disk, the outer-most disk. The PO had put it on the upper one in the pic.
 

As you place the small disk inside the larger disk, make sure the three nubs on the inner rubber seal fit into the three holes/notches in the metal disk. This again aligns the vent holes 180 degrees from one another.
 
Stack your two larger disks as shown, and then invert them on the center post of the cap.
 
 
Press the stack down and attach the large E-clip. Again, replacing it is a good idea. I wanted to get this done ASAP for the original poster, so I'm reusing the E-clip and will order the three clips directly.
 

Put the small latch spring in its hole.
 
Fit the latch button over the top. While holding that and the spring in place, insert the shorter of the two hinge pins, and cap it with an E-clip.
 
When you are ready to install the cap on the tank, fit the longer hinge pin and its E-clip.

I guess while I'm at it, I'll post up about how to rebuild the two part assembly as well, including the tear down. Again, if the mods want to move these posts into a tutorial and rename it, or put it in a different location, that's fine with me.For the caps using the two part rubber components, tear down is similar. With the cap open, remove the tiny E-clip holding the front pivot pin, and then remove the pin itself. Then remove the screw holding the keyed assembly in place. Shoot a couple of pics from a couple of different angles to help you when time to reassemble.
I guess while I'm at it, I'll post up about how to rebuild the two part assembly as well, including the tear down. Again, if the mods want to move these posts into a tutorial and rename it, or put it in a different location, that's fine with me.For the caps using the two part rubber components, tear down is similar. With the cap open, remove the tiny E-clip holding the front pivot pin, and then remove the pin itself. Then remove the screw holding the keyed assembly in place. Shoot a couple of pics from a couple of different angles to help you when time to reassemble.