If you are sure that the front bulb is OK then.......
Pull the headlight out of it's bucket and re-seat the appropriate connectors in there. Maybe apply some di-electric grease to the pins too.
You're losing either the positive or the ground to the front bulb. That's why the back one blinks too fast.
The flasher is common to both sides so, if the left side blinks OK it's not the flasher.
Good luck.
