If the front main seal (the one in the timing chain cover) is only weeping a little, I would tend to leave it alone. Time to do it is when you decide or need to replace the stock balancer with the BHJ aftermarket unit. The reason I say that is even if you install a new balancer to crank bolt (a must) you still run the risk of the stock balancer failing shortly after the re-install (been there done that). Life expectancy of our balancers is certainly fickle. I replaced 2 stock balancers on my '93 5 speed within 205,000m; yet I've just voluntarily (preventive maintenance) replaced my '94 automatic with a BHJ (along with a new crank seal) at 130,000m.