The transfer case needs to be dismantled and reassembled with a repair kit from Toyota - a standard process for this make, model and age which is described in a maintenance release from Toyota. Will a mobile mechanic be able to do this work, how long would it take, and what is the estimated cost?
My car has 186000 miles.
My car has an automatic transmission.
Rebuilding a transfer case for your Toyota Sienna is a pretty lengthy process, especially if it has not been done previously. The labor time it takes to remove and install everything for the transfer case is around twelve and a half hours.
Once the transfer case is on the work bench, it takes about three and a half hours to rebuild. I personally would be up for the challenge if you are in my area and have a place to store the van for two days, however I would strongly recommend doing research on a quality transmission shop to assist you with this particular repair.