I don't think this is a realistic offer.
On the face of it, he is offering you total assets worth around £73K
so the outcome will be that you have £73K plus income of £7.5K and no pension.
He would have assets of £49K plus income of £40K and pension of £62K.
On a slary of £40K gross he has net income of around £29,500 - I assume you have not taken into account child support in your figures? This would work out at about £4,425 (Cs is payable yuntil a child is 19, if they are in full time secondary level education) so your total net income will increase to around £11,925 and his will fall to around £25,000. You should check whether, while your son remains at home and in eduacation, you are entitled to any tax credits etc.
I think you need to look at your financial needs: What is your mortgage capacity, and how much would you need to allow you to rehouse yourself and your 17 y.o.?
What is your realisitic earning capacity? I think it is realistic to expect that you move towards full time work, but even if you are able to find full time employment your income is (I would expect) unlikly to be anything like as high as his.
I see no reason at all why you should be denied a share of the pension - this has ben a long marriage and so a start ing ppoint of 50/50 on the pension would be the norm. As you are both only in your mid-forties I presume that most, of not all of the pension was built up during the relationship.
What type of work do you do? I understand that you may ntot be able to increase your hours at present but it is likely to be reasonable for you to look at improving your income, even if this maeans looking for a second part time job if there are no more hours available in your current job, and to expect to be working full time (whether in one job or two) in the future, so one issue is to look at what you might realistically earn once you do so. I suspect that it won't be £40K but it would be higher than at present (If you were to work full time (35 hour week) even at the National Minimum wage = £10,800 gross, £9,300 net. If your current job pays above that level then obbiously your overall earning capacity will be greater.)
The fact that you might be able to earn more and to build up a pension in the future is not a good reason for denying you a share of the pension which has been built up aready.
A 60/40 split of the capital
might be reasonable
if it were to be coupled with a
pension sharing order and at this stage, spousal maintenance.