Need help with JD 50 series Investigator II monitor system on a John Deere 4050 with 466 engine.

Been bush hogging probably around 25 acres of heavy tall grass. Everything has been normal.

In the past at low idle (780RPM ) once up to operating temp the trans pressure light and question mark would light up. Increasing idle speed slightly turned them both off. Seems to be well documented issue at lower idle speeds.

Anyhow at start up turning the key on the alarm would sound and all the left hand lower lights would illuminate. Start engine and they all go out as they should. Last night shut off to add fuel and when I turned the key on no buzzer or other lights just the low trans pressure light and question mark. Start and go full rpm no change both still illuminated.

Thinking the sender may be bad ? Possible loose connection pulled by tall grass down at filter housing ?

So the questions are as follows.

1) Why no other lights and alarm when turning key on. Does a faulty sensor prevent the rest of them from lighting ?

2) How do you test this sensor simply unplug or do you need to jumper the harness leads ? or check for what voltage on wires with harness unplugged ?

3) Checked at dealer for parts. Got a sender to try but was also told it might be entire gauge cluster on the left hand side. Which surprise surprise is not available reman, Has very poor prospects for being sent off and repaired and the original is made of metal but the new is all plastic.

4) If the gauge cluster is bad is it completely worthless ? I.E will it not monitor any of the functions it us supposed to and light the warning lights and alarm when there is an issue or is it just that it will not run the start up check sequence before starting?

5) Finding a good quality used one from salvage yard apparently is sketchy at best.

Has anyone found a place that can repair these or come up with a viable alternative or have any other experiences and/or remedy's to share ?

Here it is with key turned on.

Here is full dash with engine running.

Here is the screenshot of the price of one and no that is not a typo. Hard to believe with all these tractors out there there is not a better alternative or someone that can repair them.

How much oil will be lost when changing out this sender.

Last 2 images are from a web search to illustrate the gauge cluster.

Anybody been here before and what did you do to resolve this ? Really don't want to spend 4K+ for new cluster but don't really want to run with no indicator warnings and alarms if there is an issue either.