I bought something suitable from Seals+Direct some 6 years ago. Bought 2 metres for £10. 57 still ok today.
It's on
www.sealsdirect.co.uk item code AT2007, description BRS 1505 Automotive Seal ( miscellaneous). It's still the same price today £2.53 p/metre but p&p may have gone up.
Martyn