As a winter car? By this comment I'm guessing that you live someplace where it gets cold enough to snow, so they salt the roads, which destroys your car so have have one for the summer and one for the winter.
I don't think I could recommend a 300D as a winter car in a cold climate. It's a great car, but unless they are in tip-top shape they can be hard to get started when it's cold. Also, diesel fuel needs special attention when it gets really cold outside: at low temperatures it will begin to gel unless you use an anti-gel additive with every fill-up. If you can park indoors, you can use a block heater to heat it for starting, and a tank heater to keep the fuel liquid. But if you drive it to work, chances are you won't be able to park near an outlet.
Also, the 123 body (the body style of that 300D as well as 240Ds and others of that era) has a few spots that are already prone to rusting, such as the front fenders immediately behind the wheelwells. Accumulating salt in these spots would just hasten the already-inevitable rusting.
Like I said, it's a great car, but will need some TLC if you intend to use it much in the winter.
Greetings from sunny Florida
'83 240D "Steiner"
'00 New Beetle TDI