I changed my springs last year on our 17ft 1995 Bigfoot
only because one side had settled about 1/2 inch. I "flipped" the axle which only means to move it from the top of the spring to under. It raised the trailer about 4 inches. There is a kit that Dexter supplies for this which doesn't require any welding.
The axle and springs are Standen which is a Calgary outfit. The spring dimensions are not standard compared to the ones you buy "off the shelf"
You will find a difference in eye to eye dimensions as well as the number of spring leafs. Our trailer was almost 20 years old and I was happy with the ride so why screw with success. I called Standen and they knew exactly what axles and springs that Bigfoot
used plus they had a distribution center in Vancouver where I could get the springs from.
I don't have the part numbers but Standen was first rate for info and I think maybe $120.00 bought both springs.
Unless you have spun a bearing there should be no reason to change the axle.