OK first, that "dampening" adjuster on the side of the bike is for the REAR shock only. Also, 21 lbs in the rear is pretty low, I used to run around 40psi or more.
400 ml sounds like too much oil, if I recall right I was using somewhere around 360ml. 14psi in the front shocks is on the high side, the Maximum air pressure for the FRONT shocks is 17psi. The REAR Max pressure is 72psi I think.
OK when you replaced the seals did you use authentic Yamaha seals or aftermarket?? Aftermarket are KNOWN to leak! Another thing to consider is how smooth or how pitted are the tubes?
The most common reason front forks bottom out is the springs are just plain worn out! Spring rate can change just from age being somewhat compressed at all times with the bike just setting there. I can't remember the exact price, but a new set of "Progressive" brand springs goes for less than $100, around $75 or so. Of course that's US funds, in Canadian dollars that's probably a half a bizillion give or take...