L322 range rover 4.4 transfer box leak

I have a 2002 range rover autobiography. Recently due to gear change issues the auto transmission was removed and rebuilt. After refitting the jeep drives very well but after around the first 8 miles there was smoke appearing from the front nearside. Turned out to be oil burning off the exhaust. After investigation I believe the oil is coming from the transfer box breather and running down the bulkhead to the exhaust. Any ideas on what could cause this?