Sounds like the original poster expected to find compression seals like in the 61x engines.

My guess is the compression leak is unrelated to using biodiesel. Just a coincidence.

I use a magnet to remove the injector seals. Once I did a compression test without removing the seals and they all jumped out. If they're stuck, try cranking the engine with the injectors off.

And I'm not the only one who calls them heat shields

Sixto
93 300SD

When i use the term 'shield', i mean the black plastic/bakelite shroud around the injector not the sealing washer type thing.
New metal seals were fitted but this did not cure the problem.

I could agree on coincidence if just one cylinder was affected but not all at the same time.

What appears to be happening is the injected fuel is burning quickly in the pre chamber before it should (pre ignition).
I noticed there was a slight rise in coolant temperature too, following the fill up with Biodiesel.

I have replaced the pre filter and main filter but there was nothing contained in them to warrant a problem with the fuel supply.