My view of the world is to never hold debt for depreciating assets - given where the global economy is heading it could be wise to deleverage any debts/assets and use cash to ensure you own outright your belongings (the GREN!).Will you have a plan b if you have sold the S-class and the Grenadier needs a little extra fix (of three weeks) at the local garage?
If yes —> sell it
If no. —> keep their Mercedes and finance the Grenadier
Just my opinion