rust on dipstick

I noticed lots of rust on the tranny dipstick. Is this common for a 97?

Yea, me too on my 97. Actually, it's the inside of the dipstick tube that is rusty. I wonder if it's possible to replace just the tube.

Does it just go in (like the power steering filler neck) or is it threaded?

Rust on the dipstick means somehow water is getting in the transmission, its evaporating as the transmission get hot and when you get constant cooling and warm cycles it starts to rust. The dipstick tube can be changed by loosening the holding bolt, or bolts, i don't remember if there are two or not, and the tube pulls out, like the power steering. As soon as you pull the tube out though, fluid will be coming out, so its probably a good idea to change the tube when you are changing the filter.

More importantly, you have to find the source of the water, as water in the tranmission is not good at all, and can cause damage to the friction material on the clutches and cause slipping/eventual transmission rebuild.

Unfrequent and poor transmission maintenance can also cause moisture build-up in the fluid over time, so that could be another area of moisture build-up.

Is it the dip stick with the flip top or old style dip stick?
The flip top type seals better at the top.