JimF: Great News! Ever try a 15W-40 HD oil?
Like Delo, Delvac, or (my favorite) Pennzoil LongLife?
Don't recall how many miles on your S500: are you anticipating the 2nd treatment (if over 100K) and/or the maintenance dose?
'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435