Take a look at the solder joints on the header pins of insert lamp boards ,not sure about overlay i have never used them

I've seen cracked solder joints on this light board and had to just reflow solder on those header pins. I've also had to re-pin the connector that plugs into this light board. I think those overlays are designed to go right over the top of existing artwork., but have never used one.

I've had to replace a few diodes on the bonus x board

I scraped off the insert art on mine before putting on the overlay with a razor. Takes a long time, so be aware!

For the inserts I would use a chisel placed perpendicular to the playfield and then scraped across the area.

Check the lamp matrix and see if your lights that are out are in the same row or column.

http://www.pinballrebel.com/pinball/cards/Tech_Charts/Williams_Fish_Tales_Tech_Chart.pdf

Both fairly easy tasks if you have the right tools. I replaced my connector with a crimp style connector instead of the IDE connector. Crimpers can be expensive but I brought mine home from work to do the job. Reseating the connector works to remove oxidation from the pin/socket. The connectors are are designed for a set number of removals and installations. You may find that the connector, if it it fits snug is probably okay unless a wire is not fully inserted into the IDE connector. IDE -(insulation displacement- cuts into the wire insulation to make the electrical connection.). Soldering takes a little practice but is easy to master . On the back side of light board, the side you don't plug into. Apply heat to the pin and board at the time until the solder begins to "flow" or turn to liquid and "wick". Add a small amount of solder, just a touch and then remove heat. Allow the solder joint to cool before moving onto the next pin. You can use a wooden clothes pin or the old connector to keep all the pins aligned and straight. As long as you allow each pin to cool before moving on. I hope this is enough info. I can offer more help if you have any questions. If you are still apprehensive I could send you some junk circuit boards to practice on.

If you look up FT parts on Marcos website you will find the parts you need

A crimping tool is a must have, as well as pins. You can find the tool on Amazon, pins at pinballlife