Your story is common, and that is why seamless metal gutters are so popular
and
competitive. Installers fabricate them on the spot, so there are no seams,
only gutter end caps and downspout joints. They also come in a variety of
colors.
My experience with vinyl is very disappointing. Even with the rubber
connectors, the damn things leak due to hardening/weathering of the rubber,
and thermal lengthwise gutter expansion. I found that no amount of silicone
sealant, poly
sealant, nor henry's roof compound will do the trick once the joints fail .
Metal gutters with seams are very hard to make waterproof, as well, as you
found, and aluminum cannot be soldered.