by ACourtney » Tue Mar 10, 2020 10:28 am
In answer to your questions:
1. Yes, it is sensible to seal the edges of the glass to stop moisture ingress. Before fitting it is worth priming the edges of the glass and laminate with a windscreen primer, such as 3M Windscreen Primer. SIKA 207, or Totalseal Universal Glass and Windscreen Primer. Then use a flexible, non-silicone, windscreen sealant in the seal - it is worth putting the sealant into the base of the groove of the rubber on both the body side and the glass side before fitting.
2. The easiest way is to get a professional to fit it for you, as Midasnut suggests. You will find any local windscreen fitter should be happy to fit the screen - they make more money fitting a screen than supplying one. If you do want to fit it yourself, I think on the Mk3 that rather than the cord method I would try the seal-on-first method. This is where you start by fitting the seal to the body and then work the glass into the seal. You start by working one bottom corner in and then running along the bottom edge, up the sides and finish along the top. I have seen You-tube videos where people use screwdrivers to prise the seal over the glass, that seems rather risky to me. I have a set of plastic wedges and levers that are sold for removing trim on production cars and these are safer tools to use than metal ones. The issue with the Mk3 is that the bonded in dash makes access to the lower edge of the glass and seal very difficult and that is why I think that the seal-on-first method would be better.
3. As Roy said, it is more usual to place the join to the side. More importantly it is worth cutting the seal slightly over length - say 1/8", 3mm - to allow for the rubber shrinking over time as it dries in the sun. The extra length should compress into place okay between the body and the screen.
The best lubricant for keeping the rubber fresh and stopping it shrinking is Silicone grease, or oil. However, if you ever need to paint your car in the future this will cause issues for the paint shop as the silicone gets into the pores of the gelcoat and is very difficult to remove, so you may wish to avoid that. I have read comments suggesting using vaseline, but I would suggest avoiding that, or any other petroleum based product, as whilst it may freshen up an old rubber seal for a short period, long term it is going to degrade the rubber faster. I have also heard of using olive oil, or other vegetable oils, and these are less likely to degrade the rubber whilst being easier for a paint shop to clean away. Red rubber grease is a vegetable oil based grease (with a good strong castor oil smell!), so that might be worth a go.