Export from Sibelius to MusicXML with Dolet plugin - help needed

I have a score which has been typeset for me by a friend who only uses Sibelius (not MuseScore). I need the file in MusicXML format in order to import it into MuseScore, but this friend has been unable to install the Dolet plugin. And it turns out that even the latest Sibelius internal "direct export" of XML has serious faults. In particular, it corrupts tremolos which are notated in two voices and where Voice 2 moves above Voice 1 within the same measure.

Can anyone who has Sibelius with the Dolet plugin help me by generating an uncorrupted XML export? The "direct export" defines the software version used as "Sibelius 18.7.0". I can't post the Sibelius score on this forum because it's under copyright, but I can be contacted through the MuseScore messaging system.

Many thanks in advance!