Any other Sportster owners have this problem?

Knuckles....Your problem is simple and straight forward, as for the primary vent blow-by....you have a blow left-side/primary crank seal!!!!....no if's and's r but's!!!

The main oiling/breathing system with Spoty motors is that they WILL puke oil from the breather into the air cleaner ( or a/c by-passed breather hose ), because they run higher rpm's than big twins,....HD's $hlT standard of allowable 10% ring blow-by, causes the combustion pressure to leak past the rings and over-pressurize the crankcase under the pistons, allowing the 1/4 qt oil and air in the case to get puked out through the breather.

NOW.....as for the primary, the primary is ONLY isolated from PRESSURE by the crank seal behind the front engine sprocket. If this seal is craked, chipped, dameaged, etc....it WILL and DOES allow the excessive crancase pressure to over pressurize the primary and blow that excess pressure and engine/primary oil mixd out through the primary/trans vent...as the trnas & primary are vented through the same port/hose.

I am curious XACTLY which REDLINE oil are you arunning in your SPORTY trans/primary??????

I had your EXACT problem with my 99 Buell X1 a month after I bought 2 years ago....I rode it from Phoenix to Sedona at about 115-125 mph, for 1 hour....when I got to Sedona, the rear of the bike was COVERED in oil and not a drop lost from the oil tank....I washed it of and returned home slowly, very little oil spray this time....pulled the primary apart and found the left crank seal was missing several pieces of the sealing lips.....

2 months later, I had a customer come in with SAME complaint on his 02 Sporty, pulled the primary aprart and found his seal actaully popped out.

I have some recommendations for top end work to help slow down ring blow-by, if you are in nneed of of top rebuild. These mods will not only help that situation, but give better performance and logngevity

When I rebuilt my Buell, I installed a Revolution Perf 90" kit with Stage 3 Thunderstorm heads and specialized crank work, Dobeck Fuel Controller and other minor mods.....I now have a 90 INCH Sporty powered Buell with over 140 hp and 130 ft/lbs of TORQUE!!!!!

It sounds to me like the lube may not have agreed with seals in the primary case. You did use the correct amount when you replaced it right and not over fill? If the primary was "Plumb full " as you stated, then when the oil heated up, it expanded and it had nowhere to go except out the vent tube and/or past the output shaft seal. At 45k miles, it is also possible that the output shaft seal was worn and decided this was the opportune time to leak. Oil belching is usually a sign that too much lubricant was added. I have a 2007 XL1200C and I have never experienced this situation. I change my oil every 3 to 3500 miles in both the engine and the primary. Some people say that's a bit much, but I can buy a lot of oil and filters for the cost of a replacement engine and more oil and another filter.

Good luck

Sportster Crankcase Breather

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Are you sure the lube level isn't too high now?My neighbor is a harley mechanic, if you can wait I'll ask tomorrow and post his ideas. don't award a best answer and I can see what he advises.