I think the obligation would attach to the user running the service regardless of whether they were the person who made the modification. Looking at the actual

I think the obligation would attach to the user running the service regardless of whether they were the person who made the modification. Looking at the actual text I see >License explicitly affirms your unlimited permission to run the unmodified Program. Logically you would be liable for providing a copy of the software running to your users and he or she would be liable to provide source to you. Merely placing more links in the chain wouldn't abrogate someone either you or they from sharing their modifications.