I use a tailor made parts house 8&3/4 ring gasket as opposed to RTV (too messy on the next pig change). yes you need to change the new inner seal that is leaking. I pack the spring with grease to hold the spring in place and drive it in with a circular piece of round THICK stock/drift/BFH with as few strokes as possible as each stroke increases the chance of distorting the seal. As you drive it in if it starts to tilt then move the drift over to the high side & hit it a time or two to get it back even then move the drift back to center & continue. You want your piece of round stock the OD to be slightly less than the OD of the seal so it contacts it very near the perimeter (where it is strongest). If I plan on some pig changes I slightly oil the gasket and if not then I spray it with Permatex 99MA "high tack" the red thin spray gasket/glue. EDIT You're 1/4" off & from what I gather from Doc, backing plates are 1/8" & I'd mockup some 1/8 spacers under several of the bolts on each side to space the 5 hole retainer out 1/8 from the housing flange & see if you're good