In addition to cleaning battery terminals, obviously ensure that the terminals on the starter are clean and tight (disconnect the battery before disconnecting those starter terminals!).

Oh, and check the battery ground cable and connection to the body. I forget where it's connected to on the VOlvo, but on my diesel Benz sedan, the battery ground cable is connected to the fender. I was having problems with the Benz one time: not starting after shutting down after a fairly long highway drive. The engine was hot obviously. I finally realized that the ground connection on the fender was corroded. Cleaned it up, applied Copper-ease to prevent future corrosion, re-connected, and never had a problem after. Also cleaned the contacts on the starter of the Benz and applied copper-ease there too. In some cases, for an older car, one may also consider replacing the ground battery cable, which can corrode inside and not do the job when the engine compartment gets hot.

Some thoughts based on my experience. Would be easier to check this first (if you haven't done it) than removing starter etc. (what a pain on the late 240's - had to remove one a few weeks ago!)

Good luck!