If it only slowly leaks thru the valve, then it may just be that some dirt has gotten lodged in the seat. If you had noticed the setting of the valve timing when you took it apart, that would have gone a long way to solving the problem. Anyway, it it leaks then you need to remove it and check it and the valve seat for damage or wear. You CAN remove a valve without a special tool, but a valve spring comperssor will really make the job easier. Since you have the head off you could take it to a shop for the 20 second procedure, or you can perhaps borrow a tool from a place that has a tool lending policy. Do you know how to do it?? You need to compress the spring and remove the two little keepers that are wedged in betweet the stem grouve and the holder. That releases the valve and it can be pulled out.
To check it for a bend, you can place it gently in a drill chuck and spin it. Any sort of wobble (visual or by feel in the hand) spells a new valve. If OK, then check the seating area on the valve and the valve seat of the head. It should be even and have no blemishes. The valve seat can be lapped with compound to clean it up. You may or may not know this stuff, so I just laid it out for you.
Get new valve seals while it is apart.