Don't put too much money in it. I mean a rebuilt transmission. You better get
a used one and put extra money towards your new one.
Replace tranny for a used one and do a seal at the same time. Fluid change won't help your transmission. There is going to be a problem with a used tranny. They are going to be with lots of miles on these 11-12 year old transmissions. I would check if it is possible to fit a 6 gen transmission in 5 gen.