Bear in mind that there should be no pressure under Your rocker valve cover after You change copper washers.
If You get a leak from black seals, Only changing for new ones may not solve Your problem.
If there is pressure and black seals are failing You need to change copper washers as well as You're getting an air leak from injector nest and this is why black seals are failing.
When changing copper washers make sure it's done professionally and injector nests are properly cleaned before putting new washers in.

Specifications:
Product Name: Injector Seals
Condition: Brand New
Warranty: 180 days
Fitment Type: Direct Replacement
Manufacture Part Number: 1372494, 6C1Q-9K546-BC, 6C1Q-9K546-AC, 1378433, 6C1Q-6K780-AB, 6C1Q-9M577-AB, 1495919, 6C1Q-9K546-BC, 1378432, 1980.J7, 71724128, 71794621, LR010137

Fitment:
For Citroen Relay 2.2 HDI 100 2006-2013
For Ford Transit MK7 2.2 / 2.4 / 3.2 TDCi 2006-2014
For Ford Transit Tourneo 2.2 TDCi 2006-2014
For Land Rover Defender / Defender Cabrio 2.4 TD4 4x4 2007-2016
For Peugeot Boxer 2.2 HDI 120 2006-2018

Package included:
1 * Rubber Injector Seals Kit (Same as pictures show!!!)

Note:
Due to the difference between different monitors, the pictures may not reflect the actual color of the item.

Shipping
1. Free Shipping
2. Location: Leicestershire
3. Shipping time: 3-8 buisness days via Royal Mail or FedEx.

Warranty:
Guarantee Period: 1 Years
Returns & Refunds: Customers can return the goods within 60 days of receipt and process quick refund within one day
24-Hour Support: Provide you with timely after-sale support