x2 on checking the SLS valve first. The SLS valve is also controls residual pressure which impacts strut damping. Even after replacing the accumulators on my 91 300TE the ride was inadequately damped so I replaced the SLS valve which solved the problem.

Also, it is very rare for the tandem pump to fail unless it was run dry. I resealed the TE tandem pump due to external leakage, not inadequate pressure or cross contamination issues. That particular version required a special tool to remove the pump chamber heads which I can lend to you if you pursue that path.

Once you get your SLS system up to snuff you will be amazed at how well controlled yet supple the rear suspension becomes. I wish my 01 wagon had the skyhook option which fits SLS on both axles. Mark