I'm sorry, I wasn't informed that there was something wrong with putty....
Could you please take a nice macro pic of your attempt? I wonder what the long term stability of it is like? I would imagine the texture will still be a little grainy, even after filing. I personally wouldn't bother with it and just use Milliput standard grade - I'm a big fan of the stuff and these days use it almost exclusively on my walker project. In fact just the other day I ripped off a big section of Magic Sculpt that hadn't cured properly (it's so hard to mix that stuff well and tell when it is mixed) and replaced it with Milliput.
In fact here's what I'd do on that Eldar tank he was working with:
1. Mix up some milliput and roughly fill the panel lines, ensuring that the milliput protrudes out the top of the panel.
2. Use a wet sculpting tool to smooth the Milliput down so it's
almost flush with the surface (but still protruding a little).
3. Wait for the milliput to set.
4. Use my scalpel in a scraping motion to carve the protruding milliput flush with the panel. This is quick and easy.
5. A quick sand with some 240 grit then 800 grit sandpaper.
6. Done! Once painted the seams will not be detectable.
I believe Warhound has been discussing putties with some big names in the sculpting business and is planning to share what he has found with us soon.
Oh yeah I can make that....