jarda: other than unplugging unnecessary cables and replugging two remaining cables, no. Not sure what I am supposed to check in particular. The device seems to stop routing between LAN and WAN. There doesn't seem to be problem with cables or anything physical, except perhaps power spikes. Device is able to see neighbour Mikrotik devices on WAN network (=> that kind of communication works). Device is able to see computers in my LAN (=> that kind of communication therefore works as well). It just, under undefined and rare circumstances, fails to route between those two interfaces and fails to accept connections from WAN.
Again, device can be made fully operational by switching ether1-gateway interface off and on again. Reliably, by every attempt. If there was a problem with cables/ports/youname how a mere software operation (that's what disabling/enabling interface via RouterOS commands is) could instantly and reliably fix it as it actually does? I don't need to physically approach the device, touch cables and so on to revive it. Software command issued from Winbox@LAN is just enough to do the trick.
According to this statement I am not eligible for support (that 30 days limit). http://www.mikrotik.com/support.html
. You're right though, I missed the fact this is a user / community forum with no Mikrotik staff obligation to respond.