Well, at first I don't think it's a shutter problem because I heard the shutter fires loudly and clearly. Shooting with this problem for a while, I kind of get a feeling that the shutter sound is less crisp, kind of muffled, when I take a black exposure. I was able to guess a black exposure 8 out 10 based on the shutter sound. But heck, my rd-1 makes 8 black exposures out of 10 at that stage.
By the way, I got a quote from Epson Japan in about two weeks after I shipped out my RD1. The service is brokered by Japan Exposures. They did charge me a shutter replacement. It's surely expensive but considering the other option is to have a $1000 paperweight...
¥37,527 (¥30,740 parts, ¥5,000 repair, and ¥1,787 tax)
¥1,500 (domestic shipping to and from Epson)
¥3,200 (EMS shipping back)
¥5,000 (Japan Exposures fee)
¥2,100 (PayPal fee)
The Paypal fee is waived by paying with gift. Another $30-$50 is also needed to send it to Japan.