Leaks in these older "gate valves" are common, and the usual (temporary) fix is to tighten the "bonnet" or "packing nut" as you have done. Sometimes the position of the valve (fully open or not) affects the leak. Longer term, you can re-pack the valve (a fairly simple operation) or replace the valve with a new ball valve. If you're going to replace the valve, you might as well do all 3, basically building a new bypass-valve assembly. But, if you've stopped the leak with a simple tightening of the packing nut, you're probably good for another 10 years.