I suppose it could be an antiskate setting issue, as jameswei suggested. If in fact AS is set so high that channel balance is shifted to the L, you would probably also hear some R channel fuzziness or distortion, particularly on dynamic tracks near the outer grooves. Is this the case? If so, try reducing AS a bit. (On your JMW that means, unfortunately, unplugging the tonearm wire and giving it a counter-clockwise twist before plugging it back in. AS "adjustment" is not one of the JMW's stong points.)
That said, I'm inclined to another solution. You changed the angle of your C/W, which changed the azimuth of your cartridge. (That's how azimuth is set on a unipivot.) Incorrect azimuth affects crosstalk, which of course can shift images L or R. It seems fairly likely that the different sound you now hear is related to the change you just made.
You say the cartridge appears vertical when viewed from the front, but which part of the cartridge? The part that matters is the contact area of the stylus in the groove, which may or may not be aligned vertically with the cartridge body. This is very difficult to see. Dropping the stylus on a well-lighted mirror helps if you want to check visually. Another way to check, of course, is simply to return the C/W to the angle the dealer chose and listen. Many cartridges are not built square, including some much more expensive ones than your Red. It's quite possible your dealer was compensating for this.
That said, I'm inclined to another solution. You changed the angle of your C/W, which changed the azimuth of your cartridge. (That's how azimuth is set on a unipivot.) Incorrect azimuth affects crosstalk, which of course can shift images L or R. It seems fairly likely that the different sound you now hear is related to the change you just made.
You say the cartridge appears vertical when viewed from the front, but which part of the cartridge? The part that matters is the contact area of the stylus in the groove, which may or may not be aligned vertically with the cartridge body. This is very difficult to see. Dropping the stylus on a well-lighted mirror helps if you want to check visually. Another way to check, of course, is simply to return the C/W to the angle the dealer chose and listen. Many cartridges are not built square, including some much more expensive ones than your Red. It's quite possible your dealer was compensating for this.