Apply penetrating oil to the fittings and tube joints. Keep driving the vehicle normally, and applying penetrant to the fittings daily if possible. Most of it will smoke/evaporate off, but some will penetrate the joints. The thermal cycling from operating the engine will help the penetrating oil get to the joints. After about a week of this activity, try breaking the fittings loose. More directly applied heat just before loosening the fittings may help. For those that refuse to move, apply more penetrant and allow more time. A lot of "impossible" fasteners and fittings can be freed this way.
I've done this with plain old WD-40, and had better success with B'Laster! PB and Altlas Heat Riser Valve Lubricant, although the latter is becoming increasingly difficult to find. Kroil is also a good product for this. | 
