It's olde tyme. MoCo pretty much fixed their leakers with the Evo.

 

post #14 provides a detailed explanation.
If you have a slight weep then it will probably become a leak with synthetic.
The synthetic oil does not cause a leak but it is a lot better at finding a leak.
Do you have any leaks or weeps at this time?

 

Same in my 03 20/50 Mobil 1. Tried Redline in all three one season but tranny/was different. Back to Mobil 1 in all three.

 

Oops!!

 

Same here! Cars, trucks, motorcycles,outboards, John Deere lawn tractor, snow blower, etc.

 

Haha, if a shop told me synthetic leaks over a conventional oil........ Id find another shop......

Synthetic will give you more miles between changes. If thats what u want is extended maintenance, then go synthetic. Otherwise youre fine either way. I doubt HD states running synthetic in that bike.

 

Interesting that they would say that when most shops spin the SYN and tell you how much better it is and then charge you $15-$25 more when the product cost them $5-$6 more. (Guess the caps are harder to screw off and causes them more work)

When your 04 was built, unless someone has messed with it, Harley's had marking their spot way behind them.
Even so, if it leaks SYN, it is going to leak regular oil. There is not that much magic in it. A weep is not a real leak but if it drips, it needs a new gasket or seal.

 

Been running Mobil 1 Synthetic since day one of buying My 03 FXDL Anniversary Lowrider Dyna and other bikes without a hint or drop of leakage anywhere .I also run Spectro Primary and Transmission fluids in my 89 FXR,01 FXDX and the 03 Dyna .