Board Thread:Game Discussion/@comment-34956162-20180529222034/@comment-96.49.214.129-20180530163148

"A new Career Series, Endurance Legends, will be added to the Career to retain all of the 10 lap races from Endurance Kings. This Series will be a mixture of old races - with their Fame and R$ rewards carried over to the new series - and some new long format races."

They are adding this new Endurance Legends series to Career, not Motorsport - where only a single car is required to get to 100%. It could be quite possible that you will need ALL the LMP1 cars upgraded to a certain PR to gain access to the new 10-lapper.