Marathon or Roundabout??

I hope you don't ban me for posting so much but I am really trying to get all of this carseat stuff figured out. It seems like the more i learn, the more confused I become!!
Based on Bananza'a reply when I asked about using the Mighty Tite, I may have damaged my FPSE by using a Mighty Tite on it. So I am prepared to buy a new carseat for the upcoming baby. I also will have the lapbelt replaced at the dealership. How expensive is that?
I just bought a Marathon for my 2 1/2 yo son. Now I want to know if there is a reason I should get the roundabout instead of another Marathon. The Marathon would last 25 more lbs, so i figure it is a better deal. The Marathon also accepts infants from 5 lbs. up.
I think I will go with the Marathon for the infant unless there is a reason not to. Thx so much.

How much seatbelt replacement costs depends on the vehicle and the dealer. You will probably find that labor costs are more than the price of the belt itself!

The biggest "negative" to the Marathon is that it's taller than the Roundabout. That's good for fitting kids longer, but *can* be bad when trying to fit it rear facing in a vehicle with a smaller back seat.

I can understand why a seat belt may be damaged by a mighty tight, but how could that damage the child restraint?

More comments on replacement-

Your carseat and seatbelts may be just fine.

It is true that we do not recommend aftermarket products, including seat belt tighteners. Generally, we do not recommend anything that is not tested or approved by the child seat manufacturer. Some aftermarket products may be safe, others may be dangerous. Not knowing which is which makes the child the true crash test dummy. Unfortunately, even though some products have been crash tested, there are no regulations of any kind that have any standards that apply to these products.

In your case, there is a small chance your seatbelt could have been damaged. If you see fraying or other damage or are concerned for any other reason, do have it inspected by a dealer. The appearance of a tag near the anchor of the belt that advises you to replace it would also be a good sign (some seatbelts have stitching that breaks under tension in a crash and reveals such a tag). The dealer should be able to inspect it properly for any damage (much as they have to do when repairing vehicles in serious crashes), and you may not have to replace it at all.

I would find it much less likely that your carseat has been damaged. Plus, your FPSE has a metal frame that should not be as susceptible to stress damage like plastic. Unless you see obvious damage, the carseat may be OK. Obviously there is no way to be 100% sure, so certainly replace it if you are concerned if only for peace of mind.