I have always used Synthetic in all my bikes and have never had any problems. I say use what you feel is the best oil for you and as long as you change it on a regular basis you shoulnd't have any problems.

 

Syn3 installed at 1k. Will change all three holes to Amsoil 20x50 next rainy day that I am home. Also run Amsoil in my old z1 900. Cooled that thing down big time!

 

Well started with syn 3 @1000 miles check up. At 10,000 miles changed to Amsoil in all 3 holes. Wasn't happy with syn3 ,bike run much better.And I never thought it would of made that much differents!

 

I had my RK switched over to Syn3 at its first service. I'm planning to switch to either Mobil1 V-Twin or Amsoil next go-round.

 

Definitely use snythetic . HD has since realized the advantages and started selling and using their SYN-3 oil.
The absolute bestsynthetic oil on the market for your bike is Amzoil 20w-50w. It is recommended in all 3 places on the Harley
Read up on it and you will see that no other oil, can compare or beat its numbers when pertaining to heat .friction,viscosity breakdown
I use it but I don't sell it even though it sounds like I do. Maybe I should . Amzoil.com will get you to a local dealer near you.
I have a friend here in Florida that noticed a 20degree drop in oil temp when switching to Amzoil from SYN-3. Syn -3 is good oil butHD sells it for $10 /quartat the dealer ,if you can afford that Amzoil is about 9.25/qt.

 

AMSOIL snythetic 20w 50 in the motor, primAMSOILsnythetic Gear 80w 90 in the trans Dumped the SYN-3 today. Trans shifts way better now!!!! Motor runs cooler

 

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Amsoil in all 3 holes.

 

Switched from SYN3 to Amsoil last summer and couldn't believe how much quieter the engine ran. Redline in the trans.

 

amsoil in all 3 holes
20w50in 2 and 75w90 in trans
amsoil in my diesel suvs