Cannot easily find the service data for this particular model (or the Stella version) on the Vintage Radio Service Data above.
Can be downloaded from various sites such as:-
https://elektrotanya.com/philips_el3.../download.html
and freeservicemanuals.info/en/servicemanuals/download/Philips/el3549a.pdf
But can only easily find Dutch versions
Drive belt replacement is often not covered in R2R service manuals, do not know about Philips though.
David