Cannot confirm success specifically with the NP129, but the guys over at Extreme Parts Automotive (formerly SmartParts) may be able to help you. I inquired with them recently about rebuilding an NP229. They told me that it was possible, but only if they had one to rebuild, so you may have to send yours in. Give them a call. They may be able to help. Their website and phone number are listed below.
As an aside, they informed me that Advance Adapters buys their transmissions, marks them up, and then resells them. I consider that vital information.
https://spprecision.com/1-888-995-7278
Hope this helps!