yes. that's the gears.

They are a bit cheaper here:
http://www.britishpacific.com/search.php?q=GPK001

 

But the link he included also had the front cover gasket and the front crank seal.

 

Well so it does. That's easy to fix...
Land Rover parts, spares, Land Rover accessories - Search results for ERR7280
Land Rover parts, spares, Land Rover accessories - Search results for ERR6490

 

So, I ask again; should I bother flushing the engine out, or should I buy some oil pump gears and then flush the engine? Is this a common problem with this model?

I don't want to "waste" time and money. I don't want to cause any further damage. I just want to get it fixed up.

 

Common with this "model"? They are all the exact same engine, from 1989 upto 2004, same same, exact same block and heads, guts too.
Only difference is the pre-'96's use a dizzy (distributor) and the bore and stroke are changed as the engine gets "bigger", thats why if you pay attention when shopping for parts on Rover parts web sites they will say "fits years '94-'04"
The first Disco was sold in '89 but not sold in the US until '94.
Anyway...if the oil psi is dropping as soon as the rpms climb then I say its a weak oil pump.
It would not be a bad idea to do a engine flush first and then replace the oil pump gears.
And then use a good oil filter, like a MANN and good motor oil, like diesel oil.

 

it's hard to say. I tried heavy duty diesel engine oil and multiple flushes and stuff on mine, before I had the gears changed out.... but my light only came on at idle, and I didn't really have a problem, other than a bad switch.

You could always pull the valve covers and see if it's pretty sludged up.

I wouldn't drive it for too long with low oil pressure, so the flush might be kind of hard to do.

 

So the gears fixed the problem? I don't think the switch is the problem. No according to the mechanical gauge readings.

 

The blocks are a little different on the 95 and older, they upgraded the size of the crankshaft journals and used cross bolted main caps when they changed the name to 4.0L. The 3.5, 3.9, and 4.2 all have the same basic block, and the 4.0 and 4.6 are basically the same.

 

Well... I went about it wrong.... after I threw way too much money at it, I tested the pressure myself, and it was fine. So I'm not sure if it ever needed the gears.

 

Oh, so it was the switch the whole time?