Rent charge issue

So, we are selling our house and our buyers have flagged up a rent charge issue. Basically there was a conveyance in 1895, which I have a copy of, which had a total rentcahrge of £30pa for a block of 10 terraced houses. Then later on, as the houses were sold off individually it appears that this rentcahrge was "informally" apportioned to £4 per property. This conveyance is listed on land registry but I don't have a copy of it. I have checked with neighbours and all have never paid it and a lady who parents owned the house since the 1950s has records of payments until 1981 at which point no further payment demands appear to have been made and no payments made - apparently it wasn't economical to continue collection. I don't know who currently owns the rent charge, the people listed on land registry are likely deceased and companies that previously collected payment in the 70s/80s no longer exist as far I can tell. It's not a big issue and my solicitor is saying I can get an indemnity policy for just shy of £200 but this seems steep given afaik they can only claim back 12 years of payments (£48) and the rent charge will extinguish in 2037 (£44). Is there a more cost effective way to get rid of this rentcharge