Whilst recreating a missing DiskWarrior USB recovery drive for the 2008 MacBook Pro I observed with surprise that the Mac’s system was 10.11.6 but the Recovery partition was stuck back on 10.11.2. Such things are supposed to upgrade as each point update is applied.
I needed to fix this issue & did so by downloading a fresh 10.11 installer.
Running that had two beneficial effects: it reset the Recovery partition to match the rest of the System files & increased the amount of free space on the SSD from 145 GB to 160 GB. The 6.22 GB installer by this stage had been moved to another external drive so that wasn’t a factor.