I am a fan of the welbuilts. I had an original round cased one and an essentially identical abm150r (still round). I looked at some pics of yours (rectangle) that still has a round pan. I see that it still uses the same paddle. I would look on ebay for a welbuilt paddle for any machine that appears older than yours.

I see that it isn't as obvious as I thought. I believe I have found several down the page on the link below. It is the paddle that stays level (no hump) when it is mounted. You will see several being sold with the round under pan seal. The seal is not a bad thing to have when you misplace one.

Here is a link that might be useful: ebay link.

Check this site, not sure if the info is still good. I helped the original owner of this site acquire the info many years ago.
http://www.angelfire.com/ab/bethsbread/FrontPage.html
Go to ABM Parts & Service
. No this is not spam.