I searched a bit and although I KNOW this has been discussed I must ask agaion.. sorry.

My 1983 300SD with 300K miles is only showing 4lbs or so boost on my aftermarket Sunpro boost gauge.

This gauge used to read 9.5 under load.

I cleaned the hose from manifold to overboost protection to ALDA.
My line for boost gauge is after the overboost protection and before ALDA.

When the gauge stopped climbing a while back I cleaned that line again
and cleaned out the overboost valve.

Today I inspected the line from manifold to wastegte, thinking it was leaking.
While I had the tube from air cleaner to turbo off I stuck my finger in there to
see how well the blade spun, it was okay, but not spectacular...
I could give it a spin, but it did not free wheel like say - a bicycle tire.
It spun a little then stopped.

My impression is that turbos never go out. Maybe I am wrong.

I keep thinking the banjo bolt and line are clogged. But they seem really clean.

And last - the car runs acceptably good. It still is way more powerful
than the 1980 non turbo.

Before I replace the turbo I am looking for other low boost options.
Can the wastegate be bad ??

Any other things to check .
Thanks.

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250