I have the DP-SM with the 'non-servicable' driveshaft. I'm not certain if you're is identical, but I found this link on iboats (https://forums.iboats.com/forum/eng...ives/376326-grrrrrrrrr-wrong-universal-spyder) that provided the sierra part 18-6406 and besides being a total PITA to install, they worked like a champ with no vibration whatsoever.
There's a picture in the thread that shows the difference between the two.
I should clarify my statement about it being a PITA - it was no more difficult than a regular cardan u-joint except for the last one that you have to wrestle the entire lower unit to get it in a position where you can tap the caps in. If you're familiar with the process of juggling the spider and end caps (and avoiding spilling needle bearings everywhere) its a straight forward procedure.
i hate being the bearer of bad news, but you can't tell the condition of the u-joints upon visual inspection. You can tell if they're smooth and non-binding, but I've heard of folks on here say their u-joints were smooth as silk and chased a noise until they finally replaced them.
Since you already have the drives apart, you might as well replace them both. its not a matter of if they'll wear out, but simply a matter of when.
