First, AT-205 is a plasticizer. Which all manufactures use in rubber seal. It replace what time leaches out. If gunk builds on seals, it leaches out faster, drying rubber seals.
If a leak is not noticeably lower reservoir, and not wetting/soaking rubber bushing of R&P (rack), LCA, diff, etc. It can be lived with. But if leaking at output and R&P bushing are shot. I replace the R&P.
Note: ATP AT-205 was a product of ATP. ATP made rubber seals and used AT-205 in their manufacturing of seals. They were bought by Mexican Co (IIRC). The tech support is no-longer direct to ATP engineer, but just a phone room tech support reading script. I was told, AT-205 is made for them by Suncor (Sub of Phips 66),. Some on the internet are says; it's not the same as old pre being bought-out (IDK). But seems to work the same. But neither the old Co or nor the new Co ATP AT-205, has worked for output shaft of R&P (TRE boots cover).
The 200 series power steering system holds 1 L (1.06 US qts.) of Dexron II or III. For which I use Mobile 1 MV ATF always.
I do like to flushing system, before adding 1.59 OZ of AT-205. Why, flush first with full synthetic ATF

It helps clean the rubber seal, so they can absorber AT-205. Additionally, you've no idea what's fluids (types or brands) have been added over the years.
Also, if reservoirs internal screen is dirty/cologged or gunk in bottom of reservoir. I pull and clean or replace reservoir first. Which is great time to replace it's hoses, if they leak. Getting top side (reservoir and it's hose) service first. Is how I like to start diagnostic of power steering.
I posted the flush procedure for 200 series in the 200 tech section. It the same as 100 series. But I find messy to pour out reservoir, due to local.
Very good info in this thread. Thanks!
forum.ih8mud.com
100 series PS flush:
Cleaning power steering reservoir and flushing it's fluid. Keeps Vane pump and rack & pinion in top condition. These step will help you get, a better idea on how to. Power wash reservoir & hoses using a degreaser, before starting service. Makes for cleaner job. Repeat, once all done with...
forum.ih8mud.com
Over the years, I have streamlined and improved many procedures. But, don't always get the time to update or write up my stuff. Just to busy helping others. But basic are the same.