I got a writeup on how to do it. http://home.earthlink.net/~spragues/trans.htm Fairly simple procedure, should be applicable to any Bonneville (or any GM FWD for that matter). Under "harsh" conditions the manual recommends 15,000 mile fluid/filter changes, which should help keep our trannies going well past 150k.

since i do super-extra-severe service driving i change fluid every month or so. this is made easy thanks to the nipple used by the auxilary cooler i installed...just detach the flexible hose and place some 4' clear tubing at the nipple, start the engine and pour new tranny fluid in like mad. by the time i've put in 8 L worth of fluid it'* pumped out about 9. after the levels are OK, i add lucas transmission treatment.