One of our industrial customers ran his business on some vintage presses. So vintage they looked, sounded and felt like they were on their last legs with servo valves and motors failing.
The first thing we did was take an oil sample from all of his presses, analalyzed them and because the reports from the labs are written in "Greek", interpreted them in plain English for the plant reliability manager.
Normally, we'd be foucsed on microscopic particle counts (which were off the charts and found significant wear metals). In this case the paticles floating around in his resevoirs were big enough to be seen by the naked eye. So big, they were actually chunks of junk. The manager saw what had been the mystery as to why he was consistently losing $25k gear pumps. Poor contamination control practices and no regular oil analysis left him blind as to what was going on inside his machines. A widow-maker just waiting to happen.
Long story short: the oil was so old, so dirty because he didn't have filters or other contamination control measures in place over the years, that we had to recommend the dump-n-fill strategy. With the new oil however, he has new filters and plans to do in-line filtration to recycle his oil and with a disciplined oil analysis program, keep tabs on the life blood of his machines, the gear oil, to adopt a "conditioned-based", not time-based. approach to keeping his oil healthy.