I have the differential from a 1985 500SEC ready to go into our 1985 380SL. I noticed a metal plate bolted to the aft end lower right side of the back plate with the following german engraving "ACHTUNG SPEZIAL 01 SPERRDIFFERENTIAL". What is the significance? Does it mean that I have a limited-slip differential? I need to know because of the type of differential fluid I'll need to add after this thing is bolted into my SL. Since this recycled differential came to me from an out of state recycler (Silver Star) and I didn't have the fun of pulling it out of the donor vehicle, I'm not 100% certain what I have beyond what the merchant told me. Any useful input will be greatly appreciated.