Aluminum window and door repairs

I’m not sure how far window companies expand their services but usually companies that supply windows and doors usually repair them. Try Mourinho they are in Parchal near Portimao maybe a call to them they could point you in the right direction for repairs if they don’t do it themselves.  They provide aluminium windows and doors. I used to sell in Uk in my experience the sealed units in your windows may need replacing have a look at the surround of the glass the usually black rubber looking framework this may be damaged due to sun and then water ingress. If there is evidence of this damage chances are it’s new sealed units you need. The frames if aluminium should retain there longevity. Maybe ask on FB Building Renovations & DIY in Portugal. The doors you speak of sound like they may be quite old sometimes it’s the runners at the bottom of the door that need replacing. There are many different door solutions these days not least less heavy. Sometimes it’s the widths of the door frames front to back that make them heavy, try looking at how they work maybe WD 40 on the workings of the door runners might help. 
I just realised that you may have original silver coloured aluminium windows rather than double glazed so if this is the case these will have a sort of putty surround and may even have Perspex in instead of glass (I have windows like this! I plan to replace in next few months) if I look at my frames there are broken up parts of the putty) my windows are not affected much by wind exposure because of the proximity to other houses it’s a Travessa I live in and my neighbours house shelters mine. If you do have these type of single glazed windows they likely need replacing due to age and it’s likely they are no longer available. And double glazed will provide more warmth and security. 

Thanks so much for your detailed response to my enquiry.  The windows I have are double glazed and it looks as though, at some point someone has put some kind of silicon on the frame (presumably to fix a problem) which has now degraded and means it's extremely hard to full close the window.  The apartment is on a Travessa, so is reasonably sheltered, as yours is, but the water ingress happens when there is heavy rain.  

As you suspected, the doors are very heavy and have dropped onto the bottom runners; they must be about 15 years old now. 

I will contact the people you suggest and see if I can get someone over to Tavira to take a look and advise.

Thanks again.  Susan