1990 E-150 Econoline Tranny oil clear

Van has 160K miles on it with no problems at all, the tranny oil (automatic) has never been changed. It is very clean and CLEAR like very light oil but it is not pink, it never was, I was told by the ford dealer that the tranny oil was worn out and that is why it is not pink anymore.
Question, if I change it, will it ruin the tranny? several mechanics have told me if I do change it all in one shot that the seals, clutches, etc will go bad.
Should I leave it alone or take the chance.
When I bought the van it had 50K miles on it, guess I should have changed it than. ??
Thanks for any help.

Yes, you should leave it alone.
ATF contains calsium as an addative, as the ATF ages, the ATF soaks into the clutches, and the fluid gets more "grippy". When you change very old ATF, the new stuff is FAR less grippy than the old and the clutches will slip with new fluid. Ths slipping will most likely be minor at first, but the ATF will be locally overheated, which will break it down, and sooner or later the trans will fail.

This has absolutely NO affect on seals.

Thanks ModMech, I am glad I did not try to dump it and change fluid & filter, it is my wifes van and don't want to have it messed up.
Thanks again,
Bill