That sounds like a poorly designed or poorly manufactured voltage regulator. If you go back to page 3 of this thread and look at message #27, I went into some depth about how these Yanmar voltage regulators work. Please read though it before you worry about a lamp flicker. Yes, I wrote too much and much of it is kinda technically boring, but the info is good.
Bottom line is that I think the regulator design is clever, but to work right it needs to use very high accuracy components and to redesign the circuit that drives the charging warning lamp. Both of these things would fix the lamp flicker, but would raise the price of a replacement voltage regulator.
If mine ever started to flicker the first thing I would do is mount anaccessory old style analogue voltmeter in the dashboard. Simply connect the voltmeter across the battery terminals. Now if the warning light flickers you can watch that meter and see if it is staying above 13 volts. If it is, take out that charge warning light bulb and carfully put it away somewhere it is more useful. Like in your toolbox junk drawer....

rScotty