John and Mark -
I am very curious about these seals for several reasons. Before I go any further, I'll explain that my work experience on these BDs is probably 75% 1978 and newer machines, as that was where the business was when I was so busy with these in the 90s.
It was my understanding that only the short centerpost machines (again 1978 and later) ever got two bearing seals, though it makes sense that the 1974 large cap. re-design got them too as this centerpost is also potentially "under water" in high-filled tubs.
I have always thought that what allowed some of the earlier standard capacity machines to live on long enough to kill their bearings so completely was that the centerpost was tall enough to keep the bearings largely dry even with bad seals and high water levels. It may be time that I adjust my thinking on that.
I have always been prejudiced against the short post, 1978 and later machines because of my experiences with battle worn machines that "spilled their guts" all over the cabinet innards due to so much water contaminating the centerpost and transmission. I have not seen this to that extent in in any pre-1978 machine, but that truly may have just been coincidence or luck of the draw.
I have come across only one machine, post 1978, that truly had worn bearings that came close to approximating bad bearings in older models. I have attributed this to physical forces being far less in these machines because the bearings are much closer together vs. the older arrangement. Spinning slightly off-balance loads puts pressure on the top bearing due to where the tub drive block is located. This pressure increases as leverage on the bearing increases with the length of the spin tube. Maybe I am whacky there, but that is what I always blamed as the primary reason for bearing wear and failure. It does seem perfectly plausible and logical though that seal failure, allowing water into the bearing, would only wear them that much faster.
On the one 1978+ machine that did really need bearings, it was a 1983 WP standard tub machine that was only 9 years old at the time. Its seals had failed very early on, with the entire cabinet, transmission, and even the motor were covered with thick black goop. I had to use engine degreaser to get rid of it off the cabinet. When taken apart, the bearings were worn paper thin, and there was no shinny surface whatsoever on any part of the spin tube that made contact with the bearings. These bearings were so worn thin that we could not get a bearing pullers 'teeth' on them, but we soon found that they had been so heat baked by friction that what was left crumbled out like dried up rubber. I didn't need any tools to get them out of the centerpost!
One last item related to seals - I am looking forward to experimenting on how to get both of those seals out of a spin tube without taking the bearing underneath them along with. I too am a purist, to the nth degree, and my 1986 BD that I bought new has failed seals, but the bearings aren't worn enough, not in my view anyway, to warrant replacement. I'd prefer to go in there, take the seals out, and replace vs. doing half or all of a bearing job needlessly.
Anyway, I'm looking forward to working on the machines this weekend John, but keep an eye on that 518 - I might just tuck it into my carryon luggage when you're not looking!! Where is Hermione Granger when you need her "undetectable extension charm"? (Harry Potter humor).
Gordon