Not hearsay; Completely true. Pennzoil is guaranteed to create sludge in under 3k miles, or they will give you your money back. Also, Pennzoil Platinum uses synthetic parrafin wax, which will sludge up a motor faster, with it's patented ADCM's (adaptive sludge creating molecules).
Here's a picture of what it did to my engine in 3k miles.
Never use Pennzoil.
Seriously though, Pennzoil is great oil. The above is simply my attempt at jest. There MIGHT have been something to the sludge rumors from 30-40 years ago, but probably not. Use Pennzoil with confidence. It does not contain high levels of Parrafin, or any other type of WAX. It will work perfectly fine in any engine, as long as you use the specified API service category oil, of the correct viscosity.