Random drops in oil pressure when i press on the brakes

[Acoldtruckproject]

So i have a 72 c10 with a 350 engine auto trans with very random oil pressure fluctuations, mostly they happen right when i shift or when i decelerate to low speed from highway driving. There is an oil leak which seems to be from the main rear engine seal which could be the culperate, but i also had to replace a broken check valve in the power brake booster, so im wondering if theres a step i missed when i put the new valve on. Also my in gear rpm will fluctuate nearly 200rpm in total when sitting at stoplights and the like. Any ideas will help, thanks.
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[special-K]

Is it getting low on oil?

[LockDoc]

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Does it do it when you turn corners too? Reason I ask is that my Blue '67 with the 454 started losing oil pressure when braking, accelerating, and turning corners. Finally figured out that the screen assembly had fallen off of the oil pickup tube in the oil pan.... If I filled it one quart over full it didn't do it. Hey, don't laugh, I made it home without trailering it...

LockDoc

[RexDodge]

You can get a little oil pressure fluctuation with rpm's changing but not wild swings. The rpm's floating at stop lights could be a vacuum leak. What carb are you running? Quadrajets (any carb really) can develop vacuum leaks at the shafts when they get aged. It will suck air in and mess with things.

[ole dollor]

you said you had an oil leak at the back of the motor, look to see if your oil pressure sending unit might be leaking...maybe a bad sending unit, other sounds like the others said , look for vacuum leak, if it just started after working on it , look in that area....

[ChevLoRay]

Long-standing rule of thumb says, "10-lbs of oil pressure for each 1000RPM's".

My '67 Impala had a 283, that was well past its prime. Cloverleaf ramps would make the idiot light come on if it was a quart low. The fact that I had to put non-foulers on some of the plugs just proved how much past rebuilding/replacement it really was. But, it never failed to start and it always got us where we were going, and back.

When the top was down.....who knew?

If your oil pressure goes UP when you let off of the gas...that's supposed to be a sign that there is wear on your main bearings.

But for the sake of knowing...I too would look at your sending unit as well as the wire to it. If the wire is original to the truck, there could be a crack in the insulation or missing insulation that lets the wire ground out momentarily. Look for a slack spot in the wire and check where it goes thru the firewall.