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Thats your standard Eaton 12T Positraction...(12T is the 12-Bolt Truck unit) They are a limited slip unit that uses those springs to preload clutch packs on each axle. They've been around since the early 60's and are still the best posi unit out there. The new units are designed stronger with more meat in the carrier. They are all tuneable and rebuildable as well and will live long with regular maintenance...The later designs like the "Gov-Lock" and the Tru-Trac will shell out before an Eaton Posi will. The one you have there is past due for a gear lube change. Get a can of brake clean and with a catch can placed under the carrier housing, spray everything clean. If you put a set of jack stands under the axle you can rotate the carrier to get everything clean. You'll need a Truck 12-Bolt cover gasket, (Fel-Pro#93-921) and two quarts of a quality 80w-90 MP Gear Lube with a GL-5 rating. You dont want a synthetic oil in there because those clutch plates are already broken in and soaked with conventional lube. You will also need a 4oz. bottle of Limited Slip Additive. After you spray everything clean use compressed air to blow it clean and dry. Once the cover and housing mating surfaces are clean and dry apply a thin bead of silicon to the housing cover surface and apply the gasket. One more thin bead of silicon on the cover and button her up. On the forward right side of the housing you will see the filler plug, remove it and squirt the 4oz. bottle of Limited Slip Additive in first then squirt the Gear Lube in. The GM 12T will take about 1- 3/4 quarts, fill until it begins to run out the plug hole and replace the plug. Your done! There'll be a swarm of guys that will say "you dont need the gasket" others will tell you to "use synthetic oil" because it withstands heat better than conventional oil. I already explained why to use the conventional and heat is never an issue with a high mileage differential. One detail I almost forgot, make sure the vent is open, it is located on top of housing and should have an 1/8" barb for a small rubber tube or a small plastic tube with a breather cap. The vent must be open to allow the differential housing to breathe. Heres an example of the correct lube and additive, https://www.oreillyauto.com/detail/v...c10-pickup-rwd https://www.summitracing.com/parts/a...SABEgJSovD_BwE