Steering Problem 1997 Pulling hard to the right.

This Van seems to have a natural pull to the right because I have had this problem for years. Wheel alignment never fixes it, but makes it better for a very short time. Now the problem seems to be extreme right after I rotated the tires. I only rotate tires front to back, back to front, but I noticed the manual says your supposed to cross rotate also? I seemed to have gained some vibration also. Every time I have an alignment done, it never drives straight, always pulls to the right. The shop I trust replaced upper and lower ball joints on passenger side about 20,000 miles ago. That seemed to be the best fix for about 3000 miles and slowly got worse and worse again. Almost scary to drive. If you let go of the wheel it is over one lane in seconds like your trying to steer it there. Last alignment was 6500 miles ago. I removed the brake caliper passenger side and decompressed it then compressed it out completely 7-8 times and lubricated with motor oil under the dust boot. Does not seem like the brake caliper is the problem. If anyone has any ideals would really appreciate it.

I see a few things to look at, both in short term and long term. First, if problem changed when tires rotated, you might have an internal problem with the time, one you probably may not be able to visually notice. Exchange the tires left to right on the front, and if the problem follows the tire, it is defective. Also check for a bent rim.
When you had front end alignments, were they 2 or 4 wheel alignments. If only 2 wheel, front end may be correct, but if something is bent at the rear, it might be causing the van to steer erratically.
Finally, long term. I know you thought you were helping by lubricating the brake pistons with oil, but internal brake parts are EXTREMELY intolerant of petroleum based lubricants-oil, ATF, greases etc. They will swell and cause seals to stick or leak. If you trust your garage, talk to them about it, but I think you may be replacing the calipers

.. When you had front end alignments, were they 2 or 4 wheel alignments. ....
..would be relevant with a 4 wheel independant suspension....this is a straight rear axle only held by traction arms that have no adjustment. THe only way it could be off would be due to an accident...."something bent" as jeffrv said.

Does the van look level as seen from the front?..I have seen springs broken at one end ..making the car tilt on one side.
ALso...are you sure the rims are original and the same on both sides at the front? an after market or salvage wheel might fit the holes but with a different offset on one side will have this effect.....

Unidirectional tires (with an arrow on the side) can be only swapped front and rear...and the tire MUST rotate as the arrow indicates: verify that; but "normal" tires can and shoud be swapped left and right also.

CHeck for equal tire pressure left and right...