Double Glazing - water seeping in

Advice2017

Hi, we have very old double glazing (probably around 15-20 years).  Many of the sealed units have failed (condensation inside). 

Around one of the units which doesn't look too bad (not much condensation) we've noticed that rain water is now seeping in somehow and collecting on the inner windowsill.

Is there a way we can establish whether replacing just the sealed unit rather than the whole frame will solve the water ingress?  Don't know how to tell if it's the frame or the sealed unit? (although looking at the bottom the inner black rubber looking seal seems to have damage in each corner).

We hope not to be long term in the house, so looking for the cheapest solution that will stop the water issue.

We were going to go to Cloudy2Clear but they have mixed reviews - anyone used them and can feedback their experience?

Many thx in advance.

born_again

Any local glazing co should be able to replace the units.

silvercar

Sounds like the seal between the unit and the frame has gone. Water is getting between the two on the outside and finding its way inside.

flashg67

I had some where the rubber seal rotted between the glass and the frame causing a leak - they're cheap to have done whilst changing the glass units

ThisIsWeird

Hi Advice.
The actual glass DG units themselves don't 'leak' to allow outside water in. In fact, even when they 'fail' and allow condensation to form inside them, they are still near fully effective as insulated DG units. But that's a completely different issue to outside rain getting inside the house.
So, if you are having rain come inside, it almost certainly means you have an issue with the rubber blade seals on the frames around the units. More than that, tho', there must be something amiss with the built-in drainage inside the main frames that is allowing the frame around the DG units to fill to the point that the water pours through to the house inside.
Because, if you look at these blade seals, they often don't seal perfectly at their corners in any case, as they are simply crudely mitred. Some rain can always make its way past these seals to some degree. That shouldn't mean it comes inside, tho' - there should be hidden drain holes around the DG units, to drain away any rain that gets past the outside seals, and sends it down and back outside at the bottoms of the windows. 
So, most likely - I think - is that these drain holes are blocked, or perhaps the rubber blades seals have perished to the extent that they allow in too much rain, so the drains are overwhelmed - some therefore overflows inside too.
Pretty sure that's correct
So, expect the DG units to need replacing for cosmetic and marginal-insulation reasons at around £100 a pop?, and also the rubber seals to require renewal, and possibly the drain holes to need clearing. 
I think.

Advice2017

Thanks very much everyone or the helpful advice, especially ThisIsWeird, for the detailed explanation which helps me to understand.  I can see evidence in both bottom corners of the black seal looking perished, so what you say makes sense.  I am sure the frames themselves weren't the best quality of best installation to begin with either (!), but will get some quotes just to have the sealed units replaced and the seals around them - and see if the person doing this can at the same time clear out the drain holes.  Hopefully these will last for as long as we need to stay in the house before hopefully moving... 

Thanks again, Merry Xmas!

twopenny

Also look for window doctors in your area.
They tend to specialise in repair so are cheaper than a company with bigger overheads.
I got all the seals done on my opening  windows for £160 and she adjusted both door locks at the same time. She can have glazed units out, cleaned and replaced like lightening where I've found the companies take their time.