In the interest of saving money and keeping my '81 37 ft convertible functioning I have done the following. I can give more details if you like.
Lazaret Vent Louvers; Hard landings tend to break them loose and overboard they go. I laid up FRP, cut them painted and installed. Worked pretty well but make your mold slightly small and lay up inside of it not outside. Finish with a layer of fine cloth.Have some left over.
Port light Screens:
I stacked up copper sheets and sandwiched between 3/8 plywood and cut out two rims for each screen and soldered bronze screen between them. Use a forstner bit on the inside and sabersaw the straight lines.They look a little bright until they tarnish. Worked well but lots of work.
Helm Pump (Hynautic) rebuilds: Easy, you can buy the 4 lip shaft seal, wiper and o rings from local bearing and seal vendors. $6 got everything I needed. Take care to mark the relative position of the plastic ball bearing retainer to the stator so you do not screw up the port timing. It only works in one of the four way options.
Water Tank Level Guage: When mine corroded so badly it could not be repaired I used a MagneHelic pressure guage and a squeeze ball, checkvalve and mounted a polyethylene tube in the old site gage and made a bubbler. The MagneHelic can be re-calibrated to read in inches of water or gallons if you take it apart and make a new scale. I hung it inside the lower helm station. It indicates the tank level very accurately (+ or - 1/2 inch of water).