Oil Pump Change?

91/4.0/AW4

I'm planning on doing my rear main this weekend, and I was just wondering what the verdict is on replacing the oil pump?

I've heard if it's a cast iron one I should leave it alone but if it's an aluminum one I should replace it.

How do I know what I have before I dig in?

Thanks in advance for you guys' help.

when i did the rms on my 89, i just made sure that the pickup screen was clean and not blocked up.

i believe mine was cast iron.

how is your oil pressure?

well i think my gauge is gone because it stays at 20 psi no matter what, and I think if that was the case my 4.0 would have died by now (I've had it for 2 years and haven't been gentle with it).

It's also a little weepy around the sending unit/oil filter o-rings so I'm gonna be replacing those too I think.

Minimum oil pressure is 12. I have 20 at a hot idle and 40psi at 3000. 89 4.0 212k miles.

Mines around 40 cold and 20 warmed up. 89 4.0 with 260k miles.