If by chance the harmonic balancer has a damaged area where the seal rides, I prefer to use a Felpro Speedi-sleeve (NAPA sells them..$8.00) that slides over the damaged area (no machining needed) and is held on with an epoxy adhesive. This provides the stock seal with a "new" contact surface.
I've found that sliding the LOOSE timing cover (with new stock seal) over the renewed seal surface of the balancer CENTERS the seal surface. Once the balancer is seated fully on the crankshaft, you can tighten up the timing cover bolts. This guarantees that the seal is centered on the HB. The HB installation process is made much easier if you drill/tap the crank snout to use a SBC balancer bolt with a couple washers/bearings to PRESS the HB home.
Drilling/tapping the crank on a 235 with a battery powered drill isn't at all complicated as the snout has a cone shaped surface inside to insure centering. Being able to press the HB into place and tightening the timing cover AFTER, eliminates any potential for this pesky seal leak. It takes a whole lot less time to drill and tap than to have to replace a leaking seal, and eliminates having to use a BFH.
Dave
