Does this indicate missing/damaged damper bumpers? The clunk seems to come from both front forks...
Hopefully it is just a missing topping out bumper bush but that is the last resort when the forks hit full extension and the bush on it's own will not always prevent a clunk.
Before the damper piston hits the bumper, rebound damping should increase noticeably over the last bit of travel as the fork approaches full extension. When the rebound damping orifice which is positioned 25mm below the damper piston falls below the damper valve washer the volume of fork oil below the damper piston has no where to go except to leak past the washer. This provides a hydraulic bump stop effect and slows the fork over the last 25mm of travel.
If you stroke the forks by hand with the springs out this increase in rebound damping over the last 25mm of extension should be very obvious. If you can't feel it then either the fork oil level is low or the oil is too thin or there is too much leakage past the valve washer.
You should also be able to detect this increase in rebound damping with the springs in place but the wheel and mudguard would have to be off to stroke one fork leg at a time.
