I've had no problems using WD40. The only problem may be with some bottom brakets if solvent can contact the bearings. With Shimano cartridge style, there is no problem.
I treat the bike about once per year, in Sept, and squirt some into every hole, then tip the bike around to spread it. I just happen to have WD40 and it works. It leavs a thin film on the tubes after it evaporates.
You can remove the fork to squirt inside the TT and headtube. let the headtube dry a bit, you dont want solvent dripping onto your bottom headset race.