In 2004, the MoCo started using plastic oil tanks. There were two factory installed versions, 04-06 (62888-04 ) and 07-09 (62888-04A).
The 04-09 oil tank versions share the same basic setups as the oil tank and electrical junction box (that is vulnerable to moisture). ¹⁾
The EFI bikes use up more space in the junction box, having an additional relay and more fuses?).

Late 2009, they came out with an upgrade version (62888-04B) with a 10 PSI pressure relief valve in the top of the tank, right side.
The -04B tank fits 2004-2009 Sportsters and also has a less restrictive vent tube configuration inside the tank.

04-09 Oil Tank Upgrade (62888-04B) 2)

Article by JohnK of the XLFORUM ³⁾

If you've noticed your oil cap mysteriously popping up, it could be a broken internal sleeve.
One of the first symptoms is that the cap will not stay flush, but will protrude maybe an eighth of an inch above the tank surface.
Eventually it will not click down in place at all.
Take a close look just under the cap, where the plunger enters the body.
The black sleeve protruding above the grey body (in the right side arrow in the 1st pic below) may indicate a broken sleeve.

The sleeve should be flush around the perimeter as shown by the left side arrow. 4)	To disassemble, find the two side square tabs and push each one in, and the mechanism will pop out under spring pressure. 5)	This is what you will have, notice the ratchet spring on the side, note how it fits for re-assembly later. 6)

Now take a look at the bottom of the 'sleeve'.
It should be one piece.
The two halves are held together by two very thin sections of plastic on the bottom (as in the circled areas below).
In this case, the sleeve was broken into two pieces.

The locking tabs are both on one half of the sleeve, the other side is free to slide inside the body.
As long as the sleeve is joined together in one piece that's fine.
But the bottom thin section is prone to cracking.
(one side is locked and the other moves up and down ever so slightly each time the cap is popped)
Once this fails, the 'loose' side will protrude up as seen in the first pic above.
The side without the locking tabs is also the side with the ratchet spring.
(which adds additional up and down drag every time the mechanism is worked, accelerating the failure)

The thin connecting material was broken out. 7)	Here are all the components, minus the broken out pieces. The sleeve is now in two halves. 8)	Note the locking tabs on one half of the sleeve and none on the other. 9)

The solution was to re-assemble the mechanism and install a set-screw to hold the loose side in place.

The entire operation shouldn't take more than an hour, if you take your time.
The only items required are a small screwdriver to push in the locking tabs, a set screw, an appropriate drill bit and drill.
You can find a small flat head screw, countersink the hole and drive the screw head flush for a better-than original look and function.
¹⁰⁾

Below, a brass screw from an electrical lug was used to screw through the grey plastic body and into the black inner sleeve.
It was short enough not to interfere with the moving plunger while long enough to screw through the grey plastic body to the sleeve.
Find a way to hold the sleeve down flush with the outer body and drill a hole slightly smaller than the screw thread.
Drill it right through both the body and sleeve.
It can be done with the plunger installed but it would be better to leave it out.
Drive the screw into the plastic, it will cut its own thread (that's why you drill a smaller pre-drill size hole).

Finished product. 11)	Here's what it looks like from the inside. The spot for this particle drilled hole put the screw partially in the slot, which would have nullified the fix. A smarter choice would have been into one of the lugs as indicated below. 12)

Article by ridinfool of the XLFORUM ¹³⁾

Sometimes you have to be innovative to save some cash.
This oil temp gauge was devised for about $20 as opposed to the $45 one from the MoCo.

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Parts & Tools:
One meat thermometer either instant read dial or digit read.
Some JB Weld.
Drill / bit.

Take the oil cap apart as shown below.
Then cut the dipstick off flush with bottom of the cap.

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Drill a hole just a bit smaller than the thermometer rod through the center so it fits snug.
Then drill a hole through the top of the oil cap.
Going through the bottom, there is a plastic piece that guides the drill bit.
Slide the meat thermometer in place with some JB weld on the bottom of it so it stays in place.
(make sure not to get the JB Weld on the rod itself as it needs to go up and down with the oil cap)

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