Which seals are you speaking of that were double lip? Nearly everything I can think of offhand were CR (Chicago Rawhide) single lip with thick brass outer shell. But you bring up a good point, single lip seals only are really effective in one direction, and marginally effective in the other direction. And yes, the trend is to use two thinner ones back to back, but even if thinner they often won’t fit two in the old cavities. In such a case you use one, in the same direction as the original (lip facing the oil). That’s as good as it ever was. Besides, you sometimes can fudge a little bit and get it to a less worn area of the shaft. Needless to say, if two will fit, use ’em.
Which brings up another thing: A lot of people get hyper about a few drops of water in the oil. To my mind, it is a matter of how much, how quickly. Because of the seals being effective in keeping oil in, but not real effective at keeping water out, some water entry is not unusual. That is why the factory said to change the oil often.
.
