The little plastic T that's on the return line at the top of the fuel filter.
I think it's 191 127 247A
Wife came home with a leak, and I'm out of parts......
Hers is a '91 golf, and I know the '92 and '93 jettas take the same part.
TOok a chance and ordered two from the local altrom dealer. 15 bucks each. Local stealership wanted better than 40 bucks each. Niether one had it on the shelf, hence buying an extra one for stock.
All the USA sold ... 89-92 ... Mk2 Diesel (NA) ... had that T on the fuel filter return hose. I don't know if ECO used it or not - but probably did. Wouldn't know about 87-up Canada TD cars ... but would guess they did use it from 89-92 (maybe >?) .
I've tested 3 of these things off the car. (old originals)
Put them in the freezer for a while (20-25 F) - but could still blow strait through them.
They are supposed to divert the fuel back the filter when its cold.
Out through the bottom of the T -until it has warmed up.
I don't know the specific temp ranges.
Could you test one of your new ones ?
And see what it does below freezing ?