Keep in mind that the Double Cab in that year has a bastard master cylinder setup and is prone to leaking into the vacuum booster. With that said, you cannot buy just the secondary master that sits between the normal master, and the vacuum booster where the leak originates, and you will be looking at a $1000 plus replacement OEM booster, master cylinder, assembly. You can no longer buy the part aftermarket either. The access cab was spared this configuration, just us first gen Double Cabbers. The other failure on the 4.7 is the Secondary Air Injection Pump is prone to failure. You have to pull the upper intake to gain access for change out. I would also check the timing belt, water pump history. That is another big bump in the wallet. I am a 2nd owner of an 05 DC 4X4 and have personal experience with all these items.