With your loop type glow plugs, they rarely need replacing. What happens is that the hole that they fit into in the pre chamber gets gunked up which makes a high resistant short to ground, leaking away the current that would otherwise serve to make heat.

The answer is not replacing the plugs, rather it is cleaning the holes. Do NOT use a steel brush of any kind as small metal bits will make its way into the cylinders. Use a hardwood stick that is shaped so as to scrape out the gunk, or spring for the expensive reamer tool which makes the job quick and easy.

As for the injectors, they should not bleed off a drastic amount of fuel.

Hope this helps,