First off, DO NOT USE ether (starting fluid) with glow plugs unless the glow plugs are unhooked. This may cause serious damage to your engine. Ether should only be used as a last resort.

Now, as far as the fast start glow plugs, I don't know if the resistor on the firewall is needed with those. I can tell you that with the original style, bypassing the resistor will cause a glow plug to burn out faster.

There are one-way valves in the inlet and outlet of the delivery pump on the side of the main injection pump that are available seperately. Could be that they are leaking back and causing a lose of pressure in the system. I seriously doubt the delivery pump itself is bad. It is also possible that the main injection pump has internal leakage from normal wear or the injector tips are leaking relieving pressure in the injection lines.

These engines can be very difficult to start when around the freezing mark or lower. Engine block heaters are a big benfit at this point. On diesels, the faster you can get the engine to turn over, the better. If the engine has a lot of wear, it could be low on compression, making it harder to start. You might also try adjusting the valves, as I have heard tight valves can make the engine start harder (I assume due to lose of compression).