Here is my thread on Sun Valley
http://www.peachparts.com/shopforum/diesel-discussion/378403-sun-valley-rebuilt-transmissions-thoughts.html
I waited three years till I moved to SoCal to deal with my aging 722.3 tranny. You are in the right town. Take it to Marc. I have 20,000 miles on my rebuild and I love it. My daily driver. I did lose my neutral safety switch three months after receiving the rebuild. When I removed it I found it was a non mb clone. Marc has a good service policy and would have undoubtedly fixed it for free but I didn’t bother since it only takes 15 min to replace myself.
I had my trans swapped out with a fully rebuilt unit. They did the swap for $500 which is a deal. $2300 out the door as I recall with no goofy core claw backs. I suspect the trans will outlast my interest in the car.
I’m bad with ages I’d say he’s 50? He had a lot of 722.x in progress but the new mb trannies are filling up the place. Apparently they need rebuilding and special mods that improve durability.
My thread documents a little of what to expect. It was a one month process and I should have just bought a beater car to drive in the meantime and left the 300sd with them. Marc is one of the more interesting people I met that year. He likes to talk and you can learn a lot.