there is a small drain hole in the middle of the tube (on the bottom) make it a little bigger and stick the tube off a wd40 can in there and spray a lot..
then get a junior hacksaw blade cut it to a point at one end so the teeth form a hook and work it down the side of the bolts spraying now and again.. the bolts are thinner than the size of the hole they will be held in by compacted rust and dirt.. It took me 30mins each side to get mine out like this so I could fit a dixon bate to the car..
the garage that was going to do the job were going to drop the tank and burn them out..!
needless to say they won't be touching my car again. ;)