I thought it might be helpful to use Nathan's compilation of PD9 (below). There is surprising consistency among translations on this one.
I wanted to specifically address Cassius's:
there is clearly a "common denominator" among pleasures, and yet I do not think it is maintainable that all pleasures are the same in every respect - only in some respects.
My position is that the common denominator is simply that all things that result in pleasure is simply the fact that they bring pleasure. Sometimes for a short time, sometimes long, sometimes intense, sometimes subtle. But it's *always* pleasure.
My contention is that Epicurus, uses the "if" here at the beginning of PD9 like he uses it in PD10: If X was the case, then Y. But he implies that (I would argue from the Greek tenses/moods/grammar), from observation, we know Y is not the case (Y=pleasures don't differ; the life of the profligate dispels fears). So, things that bring pleasure are the same in that they bring pleasure, but there are many things that bring pleasure, and the job of the human is to make choices among those myriad pleasures that will lead to a pleasureable life... Which makes PD9 a perfect segue to PD10 come to think of it! Just realized that as I was writing. 
PS: So, those who attack Epicurus's philosophy for making pleasure the "highest good" are lumping all pleasures together. Epicurus is making the point that all pleasure is good (If you could lump all the pleasures together...) BUT, by the observable fact that pleasures differ, we have to decide which pleasures to choose and which pleasures to reject if we are to lead the most pleasureable life possible for us.
PD9
“If every pleasure were condensed, if one may so say, and if each lasted long, and affected the whole body, or the essential parts of it, then there would be no difference between one pleasure and another.” Yonge (1853)
“If all pleasure had been capable of accumulation, if this had gone on not only in time, but all over the frame or, at any rate, the principal parts of man’s nature, there would not have been any difference between one pleasure and another as, in fact, there now is.” Hicks (1910)
“If all pleasure had been capable of accumulation,—if this had gone on not only by recurrence in time, but all over the frame or, at any rate, over the principal parts of man's nature, there would never have been any difference between one pleasure and another, as in fact there is.” Hicks (1925)
“If every pleasure could be intensifed so that it lasted and infuenced the whole organism or the most essential parts of our nature, pleasures would never differ from one another.” Bailey (1926)
“If every pleasure were alike condensed in duration and associated with the whole organism or the dominant parts of it, pleasures would never differ from one another." (De Witt, Epicurus and His Philosophy 235; 1954)
“If every pleasure were cumulative, and if this were the case both in time and in regard to the whole or the most important parts of our nature, then pleasures would not differ from each other.” Geer (1964)
“If every pleasure were condensed in <location> and duration and distributed all over the structure or the dominant parts of our nature, pleasures would never differ from one another.” (Long, The Hellenistic Philosophers 115; 1987)
“If every pleasure were condensed and existed for a long time throughout the entire organism or its most important parts, pleasures would never differ from one another.” O'Connor (1993)
“If every pleasure were condensed and were present, both in time and in the whole compound [body and soul] or in the most important parts of our nature, then pleasures would never differ from one another.” Inwood & Gerson (1994)
“If every pleasure could be prolonged to endure in both body or mind, pleasures would never differ from one another.” Anderson (2004)
“If all pleasures could be added together consecutively with respect to space and duration, and across the entire span over which they had all existed, or at least across the principal parts of human nature <which are naturally susceptible to pleasures:> then, pleasures would not be different from each other in any respect.” Makridis (2005)
“If every pleasure were condensed and were present at the same time and in the whole of one's nature or its primary parts, then the pleasures would never differ from one another.” Saint-Andre (2008)
“If all pleasures could be compressed in time and intensity, and were characteristic of the whole man or his more important aspects, the various pleasures would not differ from each other.” Strodach (2012)
“If all pleasure were condensed in space and time, and pervaded the whole aggregate, or the most important parts of our nature, pleasures would never differ, one from another." Mensch (2018)
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