I purchased a 2014 Buick Enclave with 110,000 miles. I’ve been going through all the maintenance one by one. The latest has been the transmission. I did get it serviced, but it still shifts hard. The mechanic says he found nothing wrong. Can I add Sea Foam Trans Tune to the existing transmission fluid and drive till my usual oil change, and then get it serviced again? Then just add Sea Foam to the transmission fluid?