Just had a valve job done on a F23A head with 235k. Checked the valve seats with a flashlight before re-installing the camshaft (in a dark room) and there is light leaking through a number of the valves. The light is just barely visible. Most of the leaks are on one side or small area of the valve. The job was done by a reputable shop that's been in business for decades. Should I be going back to the machine shop to ask for refund? Thanks.

 

I would definitely be going back to the machine shop and asking how they cut the seats. Show them the gaps and ask them what's up. Then if they don't offer to fix the issue, that's when you ask for a refund.

 

Did you check to see of the rocker adjustment was tightened down too much or not adjusted at all on reassembly?
If its a full circle of light that can be seen, it may simply be the rockers are too tight.

 

Check this video -
Be sure the cam is at top dead center for each cylinder. Spray break cleaner into the combustion side and look for leaks. If it leaks, it's bad.