How to know if I need a new well pump

I have a deep submersible well that is 12 yrs. old. I have a fair amount of sediment and have to change a whole house filter once a month. The filter filled up with tons of sediment and the water stopped running before the month was out. A well man came out and drained my pressure tank and it poured out black water several times until it cleared. He said I should do this yearly. No one in my neighborhood (all on wells) had ever been told this or had done it. It's mostly back to normal, but the filter seems to be getting dirty a bit faster. The well man said I might need a new well pump or sometimes it would help to just raise it. The pressure is fine.
How to I determine if I need a new well pump, or the well casing is bad or it just needs to be lifted? This happened over the winter when I had to run a sink to keep pipes from freezing out by my well by having water moving. I have a insulated fake rock but it was -4°.

If the pump is delivering water, it's absurd to replace it because its pumping up sediment. You may benefit by lifting it up 10ft, since a submersible pump can stir up dirt up to 20 feet below it. I'd try that first.

That being said, it's 12 years old. A replacement will be needed some day. When that day comes it may be to your benefit to have the pump installers put an enviro-sock on your pump, the it will help filter out the dirt/sediment better.

No matter where the pump is, it will still lift whatever is in the water near or above the water source.

Lots of people call mineral buildup; sediment. Black water is normally a sign that you have some sulfur in your water which is totally normal. I guarantee if you remove the cartridge from that filter housing, you won't notice any difference. Mineral builds up on the pipes then gets knocked off later by air bubbles, knocking on the pipes or lower than normal pressure. It's nothing to worry about, just get used to it.

Thanks Matt and Speedbump. One question remains. Why did my house filter fill up in just a week with grit like mud that stopped the water running completely in my home and it had not ever done that before or since, although at 3 weeks now, it needs to be changed. Any thought to well casing deterioration as a problem?

What is your casing? Steel (galvanized or black) or PVC?

The reason your filter filled up quicker is that more sulfur was knocked off the pipes for some reason. Now if the material is sand, that is another problem all together. Sand will ruin your pumps impellers, plug up your washer hoses, sink strainers, bathroom toilet fill valves etc. Sand coming from the well is a major problem and could be happening for any one of several reasons.