Disconnecting transfer case

I was unaware that my vehicle had a dipstick and it's transfer case. I've been driving the car for twelve years the front started making funny noise when turning tight weather going forward or backwards. I had a mechanic looked at it and he couldn't figure it out. I had another mechanic look at it who works with Subaru's a lot he realized that my Subaru is one that has a dipstick in its transfer case. Checking it come to find out it was bone dry. I bought the oil needed to put in the transfer case ran it for one day only drained it replace the oil again drill bit for three days drained it feel it again. Explain to me the idea was to make sure I got all the metal shards out or at least as much as I could out of the transfer case so we can create more damage. Couple weeks ago the there was a really loud bang clank sounded like something breaking in the front end of the car I turned it around and went right back home I was only a couple blocks away and parked it. When the key mechanic came and looked at it again he could not reproduce the sound while driving it. After discussing the transfer case issue we had earlier we came to the conclusion that something in the transfer case had broken and settled in the bottom. He said the driving it should be fine to not tax the transmission any harder than I had to and if I had any further problems to give him a call. I've done a little bit of research and I'm not a mechanic but is it my understanding that the transportation is what controls the all wheel drive for my Subaru? And can the transfer case be disconnected? There by ending the noise I'm having. The car otherwise shifts just fine has plenty of power and behaves as should otherwise.