If the seller left you feedback, you can add a Response to it.
The most effective Responses, like the most effective feedback, are calm and factual.
And do contact your credit card company, four months is pushing it so do it now.
If you pay your PP invoices from your bank account or from a balance, add the credit card (the site is very secure) and from now on pay from there instead. Not only does this mean your seller has a faster payment, but you have that extra layer of protection.
And, in my opinion, a replacement is never a good idea. The replacement may be no better than the original and the time passing puts your ability to dispute in jeopardy. Returning the item, with Delivery Confirmation, for a refund is the better choice.