I have a stock 1998 FLHTC/I with 39k miles. I have a very annoying slow gas leak on the low pressure return line where the fitting meets the bottom left side of the tank. It only leaks when the engine is running. Could it be the check valve leaking by, or the line itself? I have already replaced the O-ring and that didn't solve the problem. Has anyone else had this issue? Thank you.

 

i had this happen to me on road king 1998...the line itself.... that line and the high pressure are under constant vibration..
the metal "nut" part itself is pressed onto the metal nipple part of the hose..once assembled ...i know of no way to separate as the metal "nut" clips one time...
consider replacement of both lines..the part munbers low 61471-95 and high 61470-95
please double check part numbers are correct for your bike....the only special tool i can remember are the internal /external retaining clip remover...less than $10 at auto part and you may wish to purchase clips #11150 (get 2) you WILL lose one.. and maybe some o-rings for fuel fittings on engine side upper 27237-95 (get 2) and center 27244-95 (get 2)...
something else..ride the bike untill tank is almost empty and then drain..remember to drain tank.. when you think it is empty, drain it again..place multifold towel on primary because regardless you will get some fuel spill..have second towel ready..and throw away towel.
i drained thru the front cross over line on a road king
i used yellow plastic household electrical wire nut to plug cross over line
i used a regular auto hose worm clamp to replace the factory press clamp on the cross over line in front of tank(clutch side) side you are working on.
hope this works for you.
with parts in hand took about 1.5 hours working very slowly with no prior knowledge and included clean-up...would have saved a good 20 minutes if i had bought the retaining clip tool..sears did not have but found it at napa(sale $4.00),harbor freight and advance auto afterwards...i had to use two O-ring picks to get clips on...