There is no banjo bolt per se in a 603. There are instead nipple fittings; one on the manifold, another on the ALDA. The line from the manifold splits to the transmission amplifier and overboost protection solenoid. From the overboost protection solenoid the line continues to the ALDA. Make sure there is a clear air passage between the manifold and ALDA. I've had no problem blowing through the overboost protection solenoid with brake parts cleaner. Don't use carb cleaner!
The upper circle shows the manifold fitting, the lower signal shows the ALDA fitting. A 12mm wrench will loosen the fittings. Do not overtighten the fittings. They break easily. Follow the lines to the overboost protection solenoid. I don't know where it is exactly in a TD.
A clogged ALDA boost signal line shouldn't cause smoke.
Sixto
87 300D