1) Personally I would start with a basic application and check the results: How is the oil changing during the clean phase and the rinse phase, and check the filter used during clean.
If the oil gets very black in both phases it may indicate a two application candidate.
But the filters may be more accurate; cut open the one used during clean and look for particles, much black and gritty particles MAY often be trapped in the filter on a sludged engine. ("Jelly-like" sludge will dissolve and not be trapped in the filter but turn the oil very black fast)
And remember the maintenance dose after the treatment is finished.
(Take a look at the filter pics Here and Here . This filter came from a BMW 316 with about 100k miles on it, no particular engine problems but some seal leaks in front and it LOVES synth oil; it drinks it up in no time... Second appl. starting these days.)

2) Stay with the existing M-1 and just change filter if the oil has still got at least 1500 miles of "life" left. No need to drive more than 1500 miles, but use mineral oil for the rinse.

Raymond
Norwegian Auto-RX distributor