[blykins]

It can be replaced by just removing the harmonic balancer. Get a seal puller to get the old one out. Drive new one in, make sure it's lubricated well on the ID before you put the balancer back on.

Also, there are centering tools that are available to make sure the timing cover is centered on the crankshaft. If your timing cover doesn't use dowel pins to locate it, it could be that it's off-center a little bit.