🚀 go-pugleaf

We're using FramMaker 5.5.6 on Windows 98. Printing is done with AdobePS4.2.3 with a Linotronic330-PPD. This combination has proven most stable over the years. But now and then we get defected PDF (destilled with AcroDist4 HighEnd.joboptions). The errors are mainly german "Umlaute" wich appear printed over the proceeding character. (����) 
To make the problem even more mystic, some of the PDFs print correctly (not all do, though), but display the errors as well in AcrobatReader 4 as in 5. 
May be we are dealing with two different error-sources here, but I currently have no hint as to what those sources could be. 
Any suggestions? 
(Newer printer drivers were tested: Errors stayed, new errors in graphics appeared, linebreaking shifted so that older documents could not be used without extensive editing) 
(The difference between those PDF printing errors and those printing okay, can also be found out by opening the PDF on a Mac. Then of course, as well as with printing you have to "see" the errors, since Sofware-Checks(PitStop) tell you, that all is well.)