Early 540s (and 530s) have a dual-filter setup. I had the dual-filter setup on my 3/93-build 530iT, then switched to the single-filter from the later models. The single-filter is the same diameter as each of the dual-filters, but is twice as long. I installed the single-filter in the lower of the two slots on the stock filter-holder.
Drew Zacharda
6-speed Touring
Originally Posted by scott540