return pump corrosion!!!

we'll I have picked up a 1000gph Reusn return pump from a buddy...
I was thinking of swapping my quiteone 6000 because it's way too strong for my retun...
beside's that;
I took the resun apart to give it a good cleaning before installing it...I ripped it aprt to only see a ton of rust and corrosion...it seem like the rust came from all the salt it had rung through with the last few years it was being used...

all the metals of the pump are now showing because the salt ate up all the plastic covers that cover up the metals in the pump...
I'll take a few shots to show ya'll...
now I'm stuck on this...btw sorry to get off topic but i need to know If or what size pump i should be running...
my tank is 40x20x24 has a 30 gallon sump 3 feet underneath the display and I'm running to 2 return outlets using 3/4inch pvc...
can anyone qoute me what's a proper gph pump i should have...:-/

 

Sorry to hear about the pump. You will want a pump that runs at 300 gph at 5 to 6 foot head.

 

you estimated it off my measurments...
I have a catalina 1800 and it full goes at under 700gph at max...
do you think I can use this 1

of course I do have valves to compress the high output...