I remember that our scrolling friends across the pond had trouble with blades breaking, I can't remember which brands were affected, if memory serves, they were returning them for new ones. I think that a bad batch of steel was the cause.
Pictures would be helpful. It sounds like the connecting rod from the eccentric to bottom arm is too long. The stroke is determined by the offset of the eccentric wheel, I wouldn't have thought the stroke would be more than an inch.
Some sellers don't like credit cards because CC companies charge interest to the seller on purchases, they call them Merchant Processing Fees, about 3.5% I believe..
If you don't mind secondhand the look out for a Delta with the Quickset clamps, model numbers, 40-540, 40-560 type 2 or 40-570. The 560 is 2 speed, the 540 and 570 are variable speed.