My normal cleaning routine for something that needs a lot of TLC:
1. Glycerin soap (the bar kind) deep cleaning
2. Neatsfoot oil as soon as it's bone dry, rub off excess
3. Clean with a conditioner/cleaner (Lexol, Fiebing's Tack Soap, etc)
4. Lots of love with Pessoa Lederbalsam
5. Clean and condition as necessary after this routine.
The Simco's gonna get all this, plus hardware cleaning, and maybe a bit more, depending.
"The wise man thinks he knows nothing.
The fool thinks he knows everything."