Driveline vibes - u-joint or axle?

[S-Class Guru]

It's a '91 300SE with about 220K miles - very pristine.
Well, after 10 years or so fiddling with a driveline vibration that occurs only at 16-18 MPH under acceleration, I'm gonna throw some heavy expenses at it.
It's slowly getting worse, I've tried all the usual stuff like flex discs, carrier bearing, mounts, ad nauseum; over the years.
So, it's time for a rebuilt U-joint or a set of axles.

Anyone got a thought on where to spend the money first?
- axled

[S-Class Guru]

It's a '91 300SE with about 220K miles - very pristine.
Drives down the road like new - except for one little thing.

Well, after 15 years or so fiddling with a driveline vibration that occurs only at 16-18 MPH under acceleration, in any gear; I'm gonna throw some heavy expenses at it.
It's slowly getting worse, I've tried all the usual stuff like flex discs, carrier bearing, mounts, ad nauseum; over the last 10-15 years.
So, it's time for a rebuilt U-joint or a set of axles.

Anyone got a thought on where to spend the money first?

- Axles seem to spin quiet and smooth, boots good, no unusual noises or actions at all. I switched them L-R about 5 years ago, no effect.
Are the axles prone to vibes like mine?
Where to get good ones? The Chinese ones are cheap, but surely cheaply made.

- Driveshaft has had a couple of flex discs over the years, and one new center bearing. The halves are aligned within the "hump marks" as directed.
The u-joint had the little "detent" about 100k miles ago, but at last check was very smooth (too smooth I think).
Where to get the u-joint rebuilt? I'm looking at the shop in Portland that is mentioned here occasionally.

Tks,
DG

[S-Class Guru]

Oops, double post - please ignore this one, and see the next, completed one.

DG