What year is it?????
If you recheck your model number, I think you will find it's a 40MLHT, not a MHLT. This would make it a 95 model, and the Yamaha parts site http://www.yamaha-motor.com/outboard/parts/home.aspx goes back to 1984. If you are looking for the OEM service manual, it's PN is LIT-18616-01-19 available from your local Yamaha dealer.