Morning, I agree the best is transmission mixed with acetone. However second best I belive is PB blaster and a tincture of time. Spray all over valve stem and guide and wait a day, spray again and wait. Tapping on the valve head works but very large danger of tilting, bending the valve head. Not worriesome if you are going to replace the valves anyway. If valve is stuck and you do not want to hit it then use some heat, torch, or hairdryer to heat up the valve guide and usually it will free up the frozen part. Remember lots of flammable stuff to set on fire so extinguisher at the ready. Let us know how you are doing. North