Replacing the low and medium profile hatch lids are very easy. please watch the the video attached to see how it is done.

Video : Lewmar Low/Medium Hatch – Lid Replacement 

Spare parts can be supplied for all our current hatch and portlight ranges. For older hatches which are no longer manufactured a selection of the most frequently requested spares is available. It is necessary to identify your hatch/portlight to determine which spares you will need. Your local Lewmar retailer should be able to order the spares for you. If they have any problems ordering the spares please contact your nearest Lewmar retailer as listed in the Dealers section of this website.

There are a couple of styles of portlights and the attached PDF will help you work out which ones you have.

There are some small differences between the Mk1 and the Mk2 hatches. Please have a look to see which one you have on your boat. This is very important for when it comes to ordering spare parts for you hatches.

This PDF will show you the identifying features to work out what type hatch you have.

If a Lewmar hatch or portlight does start to leak it is important to establish the leak path. Where the water finally appears in side the boat is not always a good indication of the leak path. The easiest way to trace a leak is to wait for a dry day and use a marina hose. Establishing the leak path may be difficult if there is a significant level of condensation on the hatch/portlight. 
Possible leak paths are:
Under the lower frame. This is caused by insufficient bedding compound between the low frame and the deck, or the compound breaking down over time. It may also occur if the cut out in the deck is too big or the hatch/portlight is not mounted on a flat surface. This is a build or installation problem.
Between the lower frame and the rubber seal (gasket). This may be caused by the upper frame being distorted or a loss of seal pressure. Lay a straight edge along the sides of the hatch and also diagonally across the lid to check for twist. Also check the seal for dirt or damage. Try closing the lid down on a sheet of paper. If the paper can be slid out when the hatch is closed the seal is not compressing.
Through the holes in the acrylic used on some products to fasten the handles, hinges or friction levers. The handles have a standard O-ring under the plastic moulding on the outside of the acrylic. This should be cleaned and lightly lubricated with silicone grease.
Between the acrylic and the upper frame. (Not Standard portlights and Concept hatches.) This is caused by a breakdown in the adhesion between the sealant and the upper frame or acrylic. Try gently pushing the acrylic up out of the frame and look for movement. This type of leak is the least common.

Yes. However if you cannot match up the old hatch or portlight with the existing range of cut outs, the only solution may be to build an intermediate frame from timber.

The Lewmar standard cut out sizes have remained constant, however the corner radius may have changed on certain models.

Wash the windows with warm soapy water. All solvents should be avoided as they will cause the acrylic to craze.