Hi Daniel, welcome to Topklasse. I have seen your name on the 116.org site, but as I am not a member of that site, I have not been able to respond to you. I do read some of the posts, but I can't really take a lot of notice. Now, to your problem. Sean of course, is much more of an expert than what I am, but I'll tell you what I know.
Flaring can of course be adjusted - as a rule by the modulator valve. If you are unable to effect any improvement, you will need to look elsewhere. Firstly, did your problems start after you had the radiator flushed/serviced/recored ? If your transmission worked well prior to the radiator work but is troublesome now, you will need to go a little deeper into rectifying or addressing the issue. Firstly, you will need to turn your engine until the torque converter's drain plug (an Allen key fitting) is visible from underneath. In order to turn the engine, I would suggest that you remove all spark plugs. Then, from underneath, with a heavy duty screwdriver or similar instrument, you will need to turn the converter until the drain plug is visible. Remove, and collect all oil in a container - probably abut three to four litres.
Next, you will need to drop the transmission pan (secured by four bolts), and then remove the valve body secured, from memory, by about eleven bolts. Make sure that you remove those bolts, and not the others that hold the various layers of valve body together - obviously, the filter element needs to be removed first before you can get at those bolts. Just bear in mind that you are now getting to the professional auto trans shop stage. At home just okay, but not a nice job. With the removal of those bolts - always leave a couple in place that will hold the valve body up. As well, you need to be prepared for copious quantities of oil that will continually drip down. Also, the transmission lever needs to be in the park position to enable the internal selector rod to be withdrawn together with the valve body.
Once the valve body is out, do not dismantle it. Just wash it out thoroughly in a bath of petrol and use compressed air to blow it out as best as possible. Replacement of the valve body (refitting thereof) is not a job for the home mechanic - again, it can be done, but you really need to know what you're doing. Once you've got everything back together and your problem persists, it will be time to remove the box from the car, dismantle and replace clutch packs. Unless you know what you are doing, the transmission shop once again is the place to go. Many years ago, when I first bought Gleaming Beauty, I had flaring from second to top. I was able to eliminate the flaring by adjusting the modulator valve, but that then rendered the shift from first to second too harsh. Removal and rebuilding the box became a necessity - on dismantling I found that all clutch seals were like Bakelite - useless in other words. Adjustment of bands - no adjustment for Bands 2 and 1, but 3 is adjustable. It primarily deals with reverse operation. Again, a fairly awkward job and you need to know the clearance of free play of the servo unit shaft.
Hope that helps - maybe not what you want to hear, but let us know how you get on. Regards Styria