Motorcycle Repair: Sputter and oil on rear plug, flapper valves, two different places

Question
I'm looking for some help, I have a HD 2002, 1200 XL and I'm having some problems.

It runs fine until it warms up good, approx. 20 minutes, then the thing will sputter and die.  When this happens, the Tachometer will spin (completely around).

Also, I'm getting oil on the spark plug at the rear cylinder(only) and oil blowing out the breather.

I've spoken with a few service techs where I bought it, however, they couldn't fix it and said that these problems are common with Sportsters.

If you think you have the answer to any or all of these problems let me know, it would be greatly appreciated.

Thanks,

Bart

Answer
Sounds like you have several problems.
First start he bike and go riding. When it dies remove the spark plug and holding it againt the cylinder with the plug wire on, turn the bike over. Are you getting a spark? Will the bike restart after a few minutes, or do you have to wait till its cold?
The oil on the rear plug can only be coming from two different places. Either the rings or the valve guides. You need to do a compression test to tell.
As to the oil blowing out the breather, it is a problem. What you need to do is replace the rubber flapper valves in the rocker boxes and that should cure that problem.
Let me know the answers to my questions
Mike