Hi Dave, I'm surprised nobody else has picked this up yet -- I would have thought the 1A was pretty common. I do not own a 1A, but if I did this is what I would likely do:
Remove the one single bolt about midway in the front of the sump casting below the table. From pictures I've seen it looks to be about a 1/4 - 20 or so and often with a square head. I'm thinking that's the oil level sight hole, so with that out I'd get as much as I could out through there. Then, unless you've managed to find a drain plug somewhere but it sounds like you haven't, I'd pull the side cover off. Three bolts holding it on, the one with the name cast into it. With that off I'm guessing I should have complete access to the inside of the oil sump and all the workings. I'd clean out all the crud and remaining oil, and then if nothing else wanted to be done I'd replace the cover. I tend to shy away from silicone gasket makers and use cork instead -- it works for me but whatever. With the cover back on, the only thing left would be to fill with oil again until the level came up to the bottom of the hole in the front (the screw I took out first). I don't think the sump is supposed to be full-up, the oil splashes around in there while the machine is running and picks up via the workings from the bottom. I'd probably use a 30w non-detergent oil to refill it.
So that would be my plan. Like I said, I don't have a machine like yours and never have. My only experience with Keller is my power hacksaw which in places has more provision for getting new oil in than getting the old oil out. I did some poking around looking for manuals but didn't have a lot of luck, so what I've suggested above is based solely on pictures in other posts. I could be totally off base in what I've suggested -- it wouldn't be the first time!
Good luck, and let us know how you make out. Could be useful for some other guys down the line.
-frank