How can I repair this cracked plastic caravan skylight?

We purchased a retro 1970s Viking fibreline caravan on Saturday and promptly pushed it into our carport. The crunching sounds alerted us to the height of the caravan and now I’m left with a skylight that has two extra shards and a missing shard…

The plastic is very brittle due to its age and has a coarse feel to it. Whilst I can probably glue the missing shards on, can anyone suggest a good, visually appealing and waterproof way of covering the gap left by the missing shard?

The most important thing is that it’s watertight. We live in the UK and there’s lots of rain here. Next is looks because it’s a beautifully restored caravan and it would be a real shame to just use duck tape or whatever.

Also advice for the cracks where the bolts are also appreciated!

If it’s not possible then I was thinking maybe find someone who can vacuum form a new one but that might be very expensive and time consuming!