Coil query

Greetings-
i recently acquired a '92 Jetta.
It's a well tuned ride and runs well.
The other day it died on me; i traced it to the ignition coil,
and as luck would have it, a spare coil came along with the package.
The replacement coil makes it run, but the appearance and fitment is different; using shorter bolts, has no heat sink, and is lacking a green lead that plugged into the harness to a matching red lead. i suspect that this is a lead for the tach drive.
Am i correct in this?
Is there a way to splice in a lead to the tach drive?
Do cars of this vintage have coil issues?
Are they picky about what coil is used?
Do i need to carry a spare?
Can anybody recommend a source for new OEM replacement coils?

Thanks in advance for any and all advice.

moto