Borrow to buy back service

When I was younger I left a position in the public service and cashed in my pension of 9 years at the time. I am now back in the public service for the past few years and was offered the opportunity to buy back this service at a cost of c10,000 a few years ago. At the time I raised 5,000 and paid this and now I'm looking at buying back the rest. At the moment it would cost around 7,000. I'm thinking that I should try and get this out of the way before the Dec budget as I could claim back tax on it this year and PRSI. The only thing is I'd have to borrow the money... I have just been offered a 6month rate from MB*A of 7.9% on my CC (which is currently clear). Would I be crazy to use this to buy the pension? My plan would be to immediately pay back the amount I'd receive in a tax refund and pay 100p/w till the end of the year as I'd have less PRSI and no tax to pay. At the end of the 6 month reduced interest rate I'd be planning on clearing the remainder from a top-up loan from CU (currently have a 3000 loan with them that I repay at a fixed 50 per week).

Any help would be appreciated, I really would like to get this service back as it would mean that I'd have full pension at retirement age

It may be very difficult to check this out, but at a minimum, you'll need to give details of exactly what you're buying (9 years?) and what salary you expect to retire on.

Sorry for the inadequate details. I'm buying back approx 9.5 years service. At current rates my retirement salary will be 60k, but I'd expect that to have gone up by the time I'm retiring! (Hoping that the pay freeze won't last 20yrs!
Lump sum is 1.5 times retirement salary and annual pension would be 50% of retirement salary.

Thanks